Here is my list of games where you can easily get 3 gold medals in order to level up faster.
Gold point buster (at 57,000 points) and gold survivalist (at 8 minutes):
Choose the punch as the weapon because it will give you 200 points/kills instead of the 100 points/kills for the whip & pistol. You will get a free life at 30,000 points (that's why you will have to choose the punch, by using the whip/pistol you are not gonna reach 30,000 points with 3 lifes = no extra free life and no 57,000 points)
At the begining of the level (and when you respawn after losing a life) pick up the gold bag (for the 1000 extra points) then quickly kill the first 6 enemies that come in two groups of 3 (for another 1200 points).
Now, simply stay inside where the gold bag was located and to the right (just left of the beds) and facing the train track (so when you punch, you will punch toward) and keep pressing the A button all the time to punch all the incoming enemies. 1 cowboy will always come from the left but you will kill him before he hits you. And 2 or 3 other enemies come from the right and up, toward you (again, you will punch them before they reach you).
Rinse and repeat this trick until the timer is over (you will lose a live after). Repeat all the above steps 4 times (3 starting lifes + 1 extra life after reaching 30,000) until it's really game over.
Gold time spender : 90 minutes
Gold medal on survivalist : When the game starts, don't press any button on the controller, just let the game stay idle. The survival timer will go down without actually playing the game. However, at 30-40 seconds from the end (that's for the bronze medal) both the time spender timer and the survivalist timer will stop, so just start playing the game until you die (try not to die soon so you can survive a little longer). At the next life, do the same thing, don't press any button, just let the game stay idle for a couple of seconds/minutes. Rinse and repeat until you have gold medal for survivalist.
For point buster, I was able to get a silver medal (at 10,000 points, gold is at 15,000). Edit: I was able to get gold on point buster. Fly slowly (by holding down the left stick or the down button on the d-pad). Just shoot everything you can, even those fuel power-ups but when the fuel is low, don't forget to use one.
The bridges/passages are used as checkpoints, as long as you destroy them and pass through, if you die, you will restart at the last "checkpoint."
Time Spender takes more time (120 mins for gold), but if you are patient, you can get a gold medal for that too.
Rack' Em Up
The time spender is short (90 mins for gold), Survivalist is 7 minutes for gold and here is a trick for that (I just got the gold medal by using this trick).
Make sure you don't lose a ball/balls during the whole game and even if you do, try losing it/them near the end of the gold survivalist timer. Hit the required ball (the one that is flashing on the table) and try to sink a ball (or 2). Now, aim the cue to the bottom, middle edge of the table, press A, leave the + target to the middle, press A again and wait there, do not press the A button for the level meter. Wait until you hear the countdown sound and the game will make the shot for you. Repeat all this 1 more time.
The number of shoots now should be 1 and the number of balls should be 2 (if you sank a ball or two, if not it should be 1 too). Now you must hit again the flashing ball and also sink one or more balls. This will reset the shoot counter to 3. Rinse and repeat this trick until you reach the gold survivalist time (7 mins). Try not to foul (in any way) because you will lose a ball.
For gold point buster, try to sink 3 or more balls in 1 shot, then foul twice. Or sink 2 balls, twice in a row. I got 80-85 points by sinking 2 balls in a row. This will give you the gold medal (at 75 points or more)
Gold for point buster: At the level selection screen, choose the medium difficulty (32,000 points), then play the first 2 levels without dying (use the special weapon (X) when they are lots of enemies or if you are about to die). It will gives you the gold medal.
Survivalist: The gold medal is at 3-4 minutes I think. Do not press start at the level selection screen, let the 10 seconds goes down then play the game at easy difficulty and very slowly, killing 1 enemy at the time and moving all around the track.
Gold medal for time spender is at 45 minutes
Gold survivalist: Simply destroy 2 of the 3 cannons when you start the game, then simply move left and right all the time, avoiding the 3rd cannon's laser. 99% of the time, the laser will miss you. When you reach gold (at 10 mins) you can die or continue playing for the point buster medals.
Gold point buster : you can quickly destroy all 3 cannons by moving fast from left to right while shooting vertically. The 3 cannons most of the time don't have time to shoot at you but you must be "aligned" to them. You can earn up to 6 lives if you use this method without dying. Gold medal is at 20,000 points. I was so good at the game with this method that I scored 150,030 points and lasted ~65 minutes before giving up because it was just boring :D. If you are good at the game, you can get 3 gold medals in one play. Otherwise, play 2 sessions (1 for survivalist and 1 for point buster and time spender)
Gold time spender is at 90 mins.
Gold point buster: Simply use the exploit (press A at the left back corner) in the first level wich will give you ~140,000 points, enough for the gold medal.
Gold survivalist: Again, use the method posted here or at xbox360a. On the first level, wait until the bees start chasing you (after the 5th time). Run around (clockwise or counter-clockwise) on the outside of the level (avoiding also the purple blobs) until they start to follow/catch you really fast. At this point, they will catch you and you will lose a life. Repeat this 1 more time. With the final life, wait again for the bees to start chasing (for some extra survivalist time) you but instead of running around the level, quickly use the exploit (press A at the left, back corner), wich will gives you 140,000 points and 3 more lifes.
Gold point buster: From the starting screen, go left, try not to die. You should pick up some treasures along the way.
Gold survivalist: From the starting screen, go down and stay there near the brick wall for the whole "20 mins". The game/timer will go idle at some point so simply press A or move a little bit to continue the timer.
Gold point buster: You only need to score 750 points for gold. If you are lucky, you can get 3 times a 5x landzone somewhere in the level. Land on it really slowly and you will get 250 points. Repeat this 2 more times and you will get the gold medal.
Gold survivalist: Very easy too, simply put the ship vertically and let it go down slowly. When the altitude shows 800-900, press the O button twice to keep the ship in the air. Make sure you press it twice and not hold the O button as it will use lots of fuel for nothing. Rinse and repeat until you reach gold. Do not press O when the fuel is low as it will end the game and you will not get a medal.
Gold point buster: It's doable, just shoot everything you see including the spaceships. You need to score 15,000 points for gold (I have a silver medal for now).
Gold survivalist: Pretty hard for gold if you start losing lifes at the begining. The only trick you can do is to keep 1 or 2 small asteroids on the 1st level. Most of the time, they will not cause any problems as for avoiding them, they will simply pass by you. The hardest part is to survive the small, more agressive spaceship. You can press O to warp in the level (where you will land is random) or press [ ] + left stick to move all around the level, avoiding the projectiles and of course the small asteroids. Gold medal is at 5 minutes.
Buzz Bombers (An easy 2 gold medals if you play 1-2 sessions)
Gold point buster: Use the method posted by other members. Gold medal is at 50,000 I think.
Gold survivalist: Same as for point buster, by the time you get a gold medal for point buster, you should also get a gold medal for this.
Gold time spender: At 90 mins.