Technically, the 3910 replaces the 3800, but in reality is more closely related to the 2900.
I haven't tried either the 2910 or the 3910, but I have compared the 2200 and the 2900, and it is going to come down to whether you MUST have the better performance, or if you are just looking for a solid player and don't want to spend top dollar. The fact that you are asking means you already have a doubt that you need the 3910. My 2 cents - the 2200 gave me about 90% of the performance of the 2900 and I was never disappointed by the 2200. The 2900 gives me that extra 10%, and for the additional nearly 2x cost increase, I would not say it is really totally justified. Both the 2910 and 3910 have gotten excellent reviews, so I'd say either are going to do well.