The 3880 almost always comes out looking pretty good in these analyses, because you get almost the difference in cost between the two in extra ink included. There are generally pretty good rebates on the 3880 (right now, the cost difference between the two after rebates is $290 - $839 to $549), and the ink included with the 3880 is worth about $250, so you effectively pay only $40 more for a 3880 once your rebate arrives and you use up the initial ink. The only time I'd ever choose a r3000 over a 3880 is if you needed either its limited roll support (the 3000 has very limited roll support, while the 3880 has none at all), the WiFi or the direct print capability (neither of these is really meant as a direct from camera printer, but the 3000 will do it, while the 3880 just plain won't!). The 3880 is much cheaper to run going forward, because the ink is half the price.
The 4900 is a little bit harder to justify at current pricing (although it sometimes shows up with huge rebates, and is then well worth considering (if you have the room for it). Right now, it is about $800 more expensive than the 3880, and only about $100 of that is extra ink. With the best rebates I've seen, it's only $300 more expensive. The ink IS even cheaper than it is for the 3880, but it'll take a long time to make up $800 (plus those big cartridges mean that you have to print a LOT to use them up). Get a 4900 if you really need the sophisticated roll handling, the extra gamut or the industrial-strength build. The 3880 is a well built machine, while the 4900 is a tank.