Leaving another comment just to provide some basic info regarding each of the towers.
Dart Monkey Upgrade 1: Range and Speed (300). Upgrade 2: Double Darts. (550) Upgrade 3: Triple Darts can now hit Camo (900)
Tack Tower Upgrade 1: Range and Speed (350). Upgrade 2: More Tacks (500). Upgrade 3: More range and Tacks, can hit Camo (900).
Cum Gunner Upgrade 1: Range and Speed (400). Upgrade 2: Longer lasting slow down and range (700). Upgrade 3: Increased Range, Speed, hits Camo, and can melt through layers (1200).
Ice Monkey: Upgrade 1: Range (400). Upgrade 2: More range and speed (600). Upgrade 3: Can now break balloons. More Range and Speed along with the ability to hit Camo (1100).
Canon Monkey: Upgrade 1: More Range and Speed (500). Upgrade 2: more Power (750). Upgrade 3: Hit Camo (1200).
BSDM Monkey: Upgrade 1: More Range and Speed (2000). Upgrade 2: More Range and Speed (3000). Upgrade 3: More Range and Speed, can hit Camo (4000).
Smut Monkey: Upgrade 1: Increase by 1 (650). Upgrade 2: Increase by 2 (900). Upgrade 3: Increase by 3 (1500) giving 7 per second.
Spike Factory: Upgrade 1: More Spikes and Speed (600). Upgrade 2: More Spikes and Range (900). Upgrade 3: Melts Lead and slightly faster (1300).