What towers to purchase first?

[The Bob]

I have been saving my money. In what order should I buy the towers? Or what towers are best?

[MonsterInside]

Ice tower should be the first, then the power tower.

[SundayRain1001]

i bought power tower almost last, big mistake, plague tower and gas should be near last.

ice tower flamethrower, sparkle awesome 1st gets

[Andrew Mills]

Machine Gun, Flame, Spark, Tesla and Ice Towers are great and will get you through nearly every level on Heroic by themselves. But I'd strongly recommend saving up for the Polymorph Tower as well as it's the best slow tower in the game by far.