The 3910 has better audio DACs, so better sound IF you're using the player's DACs. For video, it depends since the 3910 can give macroblocking with some displays (what do you have?). Personally, I love my 3910 for both audio and video. Best of all would be the 3930.
I have a silver 3910 I payed close to a grand for it a few years back. Its been an outstanding player, but my unit has the weak lazer syndrom.It plays DVDS but not CDs if I remember right. It can happen to these players and cost about $200 to get repaired at Denon. So watch out if you buy used or consider a extended warranty. If you want mine send me a PM its just sitting around collecting dust.
For video you're better off with the 2930. Check the 2930/3930 for issues/quirks. For audio, specs don't mean much when it comes to audio preferences and how it sounds in your room with your gear. You have to listen for yourself.
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