Can you suggest me the Epson 3880 or the 4900?
Which would you recommend me?
I would go to opposite of Eric, and get the Epson 4900.
It is more robust, with a better quality build. It has vacuum assisted paper transport, which all but eliminates paper misfeeds. It uses roll paper, it has a wider color gamut, it uses significantly less expensive ink cartridges.
I personally have an Epson 4880, purchased before the 4900 was available, and an Epson 7890. To be honest, for what you have described looking at a 7890 is a good idea if you can deal with the initial cost and the space problems.
My experience with these printers is that a 24 in carriage is very very nice. I like 16x20 canvas wraps, and the 17" printers are not wide enough. I very much prefer using roll paper and larger ink carts. The vacuum assiisted paper transport is something I cannot live without.
The biggest drawback to a 24" wide printer is that they have no auto sheet feed at all. I print hundreds of flyers and brochures on bond papers, so the 4880 is essential for my needs. Almost all photographs are printed on the 7890.
I'm not sure how BW prints are affected by the extra colors available with the 4900, and since that is important to you it is something to do some research on and know precisely what the differences are.