The convertible is extremely weathertight, really no perceived difference when the top is up. So if you like the top down experience there really is no disadvantage to choosing a convertible. It was designed as a convertible also (The coupe model was added 3 yyears later by dropping a coupe top on the convertible) so it is very rigid. So from a rigidity and weather tight standpoint no reason not to go convertible. The Coupe draws much more attention then the convertible so as a daily driver the convertible might be a better choice. The convertible top is a manual one but it works very well. If you are looking at a used car make sure to try putting the top up and down yourself. Some of them are so tight they are troublesome to latch unless you are practicied in the art.
I just traded an 06 convertble in on an 08 Coupe, but that was largely to get an ACR model, I was very happy with my convertible. You do need to be careful in the rain with either model, the torque plus the wide tire size can lead to trouble if common sense is not used, but many drive in the rain with no issues.
With our weather you should be fine except for those few days we get snow and ice. I think it's safe to say ice and Vipers do not mix well.
If you are shopping used you will get a better deal on a convertible as more were made from 06-08. There was no 07 model. The coupe has only been made from 06.
If you are looking strictly new the 08's are sold out and there are few in stock. I would second the thought of calling Bill Pemberton at Woodhouse. I have bought 4 Vipers and 3 other Dodge/Chryslers from him and have always been totally satisfied. Plus he's fun to talk to, you will learn a couple new accents and some jokes, no high pressure either.
Ford Chrysler Dodge Lincoln Mercury Mazda Nissan - Omaha Nebraska He has some nice 08 coupes in stock. Check the website.
Bernie at BJ Motors is another good reputable source, particularly for very lightly used, low mile Vipers. No one has everheard a bad word about a Bernie Viper deal, and he's only a few hours away from you.
His website is
BJ Motors - Used Dodge Vipers for Sale, Performance and Exotic Sports Car Wholesaler
If you would like to mingle with a bunch of Viper owners (like 60-80) stop by the Crab Deck on the Eastern Shore (just over the bridge a few miles) after 3pm on the 14th. We will be having our largest event of the year. Great way to see many Vipers and ask opinions. PM me if you have an interest in coming.