If you're here, I bet you're expecting some spoilers, but I'll spare you.
At the end of mission 13 ("The Belgian Problem"), you'll have a CHOICE between blowing up and saving the tower. Each choice garners a DIFFERENT achievement.
You can save at this junction or right before the mission—the save won't load mission progress, so it'll kick you back to your crib before you activate the mission. Go back and do it again for the other achievement.
Blowing up the tower adds a permanent 10% respect bonus (on all future respect).
Saving the tower adds a permanent 10% cash bonus on all future income.
If you're going for the achievements, you'll probably be in more need of cash than respect. That's the route I went.