Theres 2 main elements you need: A movement element (short cooldown) and an attack element. My personal choices for these are the terrarium and the thunder storm or sand storm. Keep these in mind in your runs, they can be a life saver.
Thanks for the attack element man, and for movement here's my rule: when in doubt, use fire or lightning. Those two elements in my comment are some you can get on the literal first round. Terrarium is short cool down, medium knock back, and strong. The storms are good because they strong and once your on the second round you can upgrade them to tornadoes if you wait to get more elements.
That's an interesting strategy. I love the Terrarium too, but personally I won't touch any of the storms because they either last too short for their long recharge duration, and so giving small damage while leaving you vulnerable, or pull enemies closer to you, which is not something you would like.
My #1 combo is Clay, Light Bulb, and Water Lily. Alternatively I used to go with Harpoon instead of Light Bulb, but the purple dudes on later maps are a lot harder to defeat with it, so I mostly use the latter now. Fire Lily is a good replacement for Water Lily when I'm focusing on damage because it recharges much faster, hence giving more frequent widespread damage, compensating its lack of protection.
The downside of this style is, of course, it costs lots of Stone.