[ProPain]

I rarely build cannons, I build heaps of guntowers.

Cannons can be good, but they are slow and can't hit up close. So when you build them, build em in your 2nd line.

Guntowers are really good, cheap so you can build a quick maze if you need to and they do a fair bit of damage. The key however is to upgrade, I try to get like 3 or 4 guns upgraded with a temporal tower close. Upgrade the temp tower at least once also. Double upgrade guntowers asap.

For air units missile towers are the way to go. Even a yellow missile tower will blast complete waves of air units to bits. I can't recall ever needing more than 1 red missile tower in any mission so far.

When missions have lots of little packed units like he swarmers I think upgraded inferno towers are good as well. Make sure you place a temporal tower close to your inferno tower for extra effect. All the grinders I played till now I just build inferno + temporal and upgraded. Maybe I built 1 or 2 guntowers for the first wave so I could build an extra tower in the maze, but after that: just inferno. Easily won them all. For later grinder missions the 'bombing tower' (concussion iirc) should work good as well.