Being in the Southeast myself, the biggest thing on my list of features in a tent is ventilation. Assuming you're staying local on your trips, humidity will be a large factor in staying dry, plus your condensation and the fact that you're liekly to be camping under a forest canopy, adding to relative humidity. Look for tents that have large sections of mesh roof (for nights that don't require your fly) or that have actual vents built into the fly fabric.

Another option would be to buy a single-wall tent, like the Tarptent models. The model I have has bug netting sewn in on all sides, which allows for great ventilation, and the drip line of the tent walls actually direct water away from the netting to keep you dry. Used TT's generally pop up in the "Buy and Sell Gear" forum here regularly.

Having a bombproof rainfly isn't really that important in my neck of the woods...I typically find myself under a fairly thick canopy when I'm hiking, and the storms generally don't last that long here. It's just a different scene than what you would find above treeline in the West. A bombproof, ground-length rainfly will also really build up condensation overnight down here, particularly in the summer!

Aside from that, everything else is just details. Tents that have pole clips instead of pole sleeves are generally lighter; the fewer the poles the lighter, and hubbed poles are the lightest of options, but also the most expensive. Set up models you're interested in and make sure that you actually have enough room to roll around, sit completely up, change clothes, etc.