Early '93's are for all practical purposes..... '92's. The only noticable difference? One digit in the VIN (and location the engines were built). If I where a betting man, at some point in the future these are going to be called "92 carryover cars" so sellers can claim they are tied to the first year of the Viper and get more for them!
About April 5th '93, the battery moved, antenna disappeared/moved to windshield, and tranny received a reverse lockout. I personally like the antenna as it is more "sports carish" to me. I'm going to have one on my car, but the car cover comment is a valid one....
I'd go for the '94, biggest improvement is the cooling system. '94 was a VERY high build year. In the RT's, I like '95's the best... most bugs worked out, and the final evolution and most refined of the side pipe cars.... specially a pin stamped "last 300 side exhaust" car.