For starters the R1900 is discontinued. The replacement is the R2000. Advancements over the R1900 are WiFi capability, larger ink cartridges (Epson claims you get 50% more printing capacity than the R1900), and better screening technology. I can see your dilemma here - with the 3880 at such a great price right now it is a tough decision.
Just last night I was testing some papers for an upcoming review to be posted here in a few weeks. Specifically I was using my 3880 and R1900 for these tests. At this point the R1900 is seeing very little use simply because I have three other printers (all pro models) that can handle just about anything you can throw at them. Well, it was nice to see again last night why I had given the R1900 such good marks before. The prints I made last night compared very well against the 3880. I'm going to say that Epson's printers that use the Ultrachrome Hi-Gloss 2 inks (currently the R2000) are just as good as what you get with the Ultrachrome K3 w/VM inks with glossy and luster media. With high gloss papers I would still say the Hi-Gloss 2 has a slight edge if you use the gloss optimizer. With Luster papers they are toe-to-toe, and with matte papers I would still prefer the K3 inks. Both printers are well built and in my case operate flawlessly. If you plan to print on matte papers and want the 17" width then the 3880 is the obvious choice. But if you are going to use glossy papers predominantly then the R2000 is the way to go especially if you want to squeeze every last bit of performance from your glossy papers.
BTW, the papers I am currently testing are not Epson papers and one in particular is a high gloss film. The print I made last night with this media was outstanding.
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