Some of the things I like about my trailer (and use a lot) are:
1. steps on the front and rear of the fenders to get onto the trailer.
2. a large eyelet on the front rail to pull a vehicle onto (or ease it off).
3. swing up ramps on a pipe. Easily slid to match the need.
4. also for ramps, angle iron frames with treated 2by, and expanded metal mesh for traction. Angle iron ramps get heavy quick, even swing up ones.
5. stiff legs on the bottom of the ramps to keep excess force from trying to lift up the rear of the tow vehicle during loading/unloading.
6. Spare tire mount on the passenger side, off the deck. Easier to change a flat on the road!
7. Swing up jack (and room to swing it and spin it w/o smashing your hands).
8. Tail light guards out of angle iron.
9. The most important item - matching the weight capability of every component (tires, axles, hitch, springs, etc). Nothing like seeing a 10,000 lb rated trailer w/ 6000 lb rated tires!
Everything else I like has already been covered.