As WhiteHellJumper said, there are stronger characters that are easier to use however chances are your best bet is a character you are comfortable with. This is the default survival where your drama pieces are selected for you so you may want to look for a character who you are comfortable using but at the same time has a decent drama piece lineup.
For starters, this achievement is for the first 50 rounds completed of survival mode and will pop immediately after you win the 50th round. I would say once you hit 50 the enemies are at about normal difficulty if they were to be compared to the chronicles mode.
The character I used for both challenges (To 100) was Broly. This is because he has a great foward Y lunge attack that you can charge to break the enemies guard, unless they use the RT ultimate guard. Charge the attack as long as you can and then lunge at the enemy. Follow this up with a backwards + B special attack where he launches himself at the opponent surrounded by green energy. With this method you can easily make it through the first 50 waves.
For defense I would suggest simply pressing RT to use a Ki guard whenever an ultimate is heading your way or an onslaught of charge attacks as I swear they hide at least 1 or 2 tougher battles in the early stages just because. Either way, as long as you hold RT and you have some energy you can block anything except a grapple with no damage taken so feel free to spam this as much as you see fit! (Keeping your energy in mind of course).