Yeah near the end we always get a ton of fat kids and once in a while we get a normal guy. You should put the spawn order of the fat kids a bit lower than the rest. Avalanche would be awesome for tower defense map.
Definate DL for me. Very original, interlocking looks great, great weapon choice, and it seems it would be semi-fair (as fair as meant to be) for both sides. Great map!
Update, I've been furiously forging an avalanche version of this map, I have a ROUGH version of it done. Go here: Bungie.net : Bungie Online : Halo 3 File Details