Dart monkeys have always been my favorite, no matter which BTD I'm playing. They always get the job done, and give you enough money to build other towers in later, more difficult waves.
Of course, they work much better when they've been upgraded a few times.
i am at level 34 in BTD, and have completed upto 159 waves in one go. last upgrade is sun god, which is UBER-AWESOME! it alone is enough to contain a stage 50 wave. but it costs too...........
