If going solo, I'd definitely go with a fiberglass egg camper (Casita, Scamp, etc...), but only you can decide if a trailer is too small or too big.
Single axle vs. double axle: Not that different. I've had both, and haven't noticed a significant difference when setup properly. The only extra concern with a single axle is that a blow-out will be "felt" more, since there's not an extra tire. On the other hand, when it comes time to replace the tires, the wallet feels it less with a single axle. :)
17 foot vs 23 foot: A little difference when towing if there's high wind, but if properly setup with sway control, it should be negligible. The smaller the trailer, the more sites you'll be able to use it in, and the easier it is to maneuver through tight quarters. Whether that matters to you is up to you.
Egg vs. non-egg camper: Eggs tend to have nice rounded fronts and backs. They slip through the wind nicely. Non-egg campers don't (especially the back - and nothing sucks like a vaccuum). All else being the same, the eggs tow a lot nicer, and usually with moderately better gas mileage.
As with many things, this is a very personal choice. The only way you'll make the right one for you is if you look around and think carefully. Take your time. (Or if you're in a hurry, buy a used trailer that's readily available with the plan to replace it after you've had the time to think carefully about what you really want.)
