V-nose or flat front?

V-nose gives extra interior space at the front and cuts drag slightly. Flat front is cheaper and marginally easier to shelve out. On the road the difference is small.

Ramp door or barn doors?

Ramp for anything on wheels. Barn doors if you load by hand in tight spaces or plan to shelve the interior wall to wall.

Can I stand up inside?

It depends on the model. Interior height is listed per unit, and a 6ft 3in interior is common on 7ft wide trailers. Check the listing before assuming.