Hi leier, and welcome to cruise.chat.com!
There are a few things to consider. First, if the ship is more important to you than the destination, I'd go with Norwegian Dawn. (I must admit that Norwegian Majesty is a very favorite ship of mine, yet Norwegian Dawn is more spacious and has more amenities.)
If ease of getting on and off the ship is important, I'd go with Norwegian Majesty. She remains docked at St. George for her entire stay, whereas N. Dawn spends part of the time at anchor. (This is "Grassy Bay.")
Bermuda itself is very easy to get around on your own. Both St. George and King's Wharf are convenient to the bus and ferry system. St. George is closer to the aquarium and Crystal Caves, while King's Wharf is closer to the beaches. Then again, nothing is truly that far away.
Let me know what you'd like to do while in Bermuda, and I can offer more advice. We've been four times, most recently in 2005 and 2006.