The differences that I can notice are (in favor to Transformer):
1. $50 difference
2. IPS Display
3. Better battery duration (without dock) between 9-10 hours (non-stop WiFi + Browsing) similar to iPad 2, the Iconia A500 have like 7 hours while doing the same, more info HERE
4. Lighter than Iconia A500, comparable to iPad 1, a little heavier than iPad 2.
5. Docking capability with double battery life, USBs and more flash cards.
Differences in favor to Iconia A500:
1. The back camera has LED flash
2. While both have great built quality, some owners reports that Iconia appear to be a little better here.
3. Built-in full USB port.
4. Thinner bezel (maybe it's not that important?)
HTC EVO 4G:
- Gingerbread 2.3.3 (rooted, CM 7.0.3)
- SanDisk microSHDC 16GB
Asus Transformer TF101:
- Dock TF101
- Honeycomb 3.0.1 (stock)
- SanDisk microSDHC 32GB