I've owned both the 2910 and, currently, the 3910. Excellent units, especially at their used prices. The video on both is superlative, I'm not sure I detect any difference there. The 3910 does get a slight nod for audio duties, so if you can spend the extra dough (typically an extra $200), spring for the 3910. I plan on keeping mine for *many* years to come...
-RW-