Unless you want to reserve a specific make from the Adrenaline Collection (or Prestige Collection or Dream Car or whatever other collections), which usually come with extremely high rates and often some mileage limits, your best bet is to just reserve your standard car and then talk to agents about upgrades when you arrive. I often go out and course the lot first before going inside to talk about upgrades so I know what they have and have a chance to think about my strategy.

Camaro SS and Mustang GT are both pretty fun and often reasonably priced as upgrades (I once got a Camaro SS convertible for free on a premium car reservation, and I later got a Mustang GT coupe for a $5/day upgrade for a week). Both of those were from a smaller airport location that I'm a relatively regular renter at and that often has a number of those types of cars in stock and often doesn't have my reserved premium car. I find it harder to get fun cars like that at larger airport locations that usually do have my reserved car in stock and are also trained to get a premium price for anything sportier/more fun.

I'm mostly "meh" on Chrysler products these days, but the Charger R/T and Challenger R/T are fun for the closest thing you can get to the big American muscle car experience in a rental fleet. Run far away from the non-R/T models, though...the 3.7s or whatever they're putting in the lower trims now are no fun at all. Same goes for the non-GT Mustang.

A very mediocre experience with a 2007-era V6 Mustang convertible soured me on Mustang convertibles, but I'd be willing to try one of the newer GTs. Can't recommend from personal experience, though.

Corvettes will be much harder to come by and will be charged a significant premium ($50/day plus) for an upgrade over your standard car reservation, and you won't have much luck negotiating that down. You may also be subject to a mileage restriction. I wanted to take a Porsche from PHX for a 4-day road trip and the agent quoted me a firm $70/day upgrade (no backing down from that) but then informed me there would be a ~100-mile-per-day limit. That wasn't going to work with our 700-mile road trip we had planned around northern Arizona. Same may go for the specialized trims like the GT-H and the like. Those are usually only available at major airports and the local staff are very protective of them.

One thing: if nothing interesting is available when you pick up, you can check back later and swap cars, or you can even go to any other corporate-operated store and swap vehicles there if they have something you like. I got a Lincoln Town Car at LAX once on a premium reservation and went over to Burbank and swapped for a much-more-manageable Hyundai Genesis.

Oh, and I know the whole "how long you've had your license" thing is big in Europe, but over here, that's not even a question. The only thing anyone cares about is how old you are (>25 is good) and when your license expires. I think it's because the vast majority of Americans get their licenses at or around age 16 and so anyone who's 25 or older is assumed to have been driving for nearly 10 years. (Also, the issue date printed on my license is about 7 months ago, but that's because I had to go in and get it renewed last year (PA licenses expire every 4 years). I've been driving for over 15 years now, but there's no way to tell that without pulling all of my previous states' driving records or something. It's simply not an issue here.)

Some threads for research:

http://www.flyertalk.com/forum/hertz...shrinking.html
http://www.flyertalk.com/forum/hertz...periences.html
http://www.flyertalk.com/forum/hertz...t-you-get.html

I don't think snow is going to be much of a concern in most of the places the OP lists.