I think either will be fine. BUT, over the years I've found Epson to be far and above more reliable and easier to use than HP (mostly in the 40"+ wide arena).
The 3880 does not have a self-calibration, built in photospectrometer. HP does ( if I'm not mistaken ). Epson offers an optional self-calibration photospectrometer on the 4990. The key for the 3880 is to get the "Designer" edition which comes with a dedicated software RIP from Efi. The HP 130 uses a third party RIP ( sold separately ). These "RIP's" can do a decent job on color matching and screening. So, if you are serious about offering a contract proofing solution, you will have to look beyond the printer itself and see what calibration options it has if any and its RIP options. The standalone 3880 and the HP130 are "photographic" printers; for a industry standard graphic arts solution, you will need the ability to calibrate and match color. No options for calibration with the 3880 although the Designer Edition Efi Express RIP does a good job precalibrated for Epson papers. Take a look at extended warrantees for anything you decide, worth the investment.
That Epson doesn't have it because at that price point, you'd be better off just buying your own Spectrophotometer (better than then one use only internal Spectrophotometer, the newer i1Pro-2). Plus every Epson I've profiled and trended has been incredibly consistent in terms of low average and max dE over time (assuming it's operating correctly: no clogged ink heads. My 3880 never clogs yet my 4900 does al the time).
IOW's, Epson's don't need calibration to remain very consistent. They could really use calibration in terms of the non linear behavior of the Epson driver which is another story.
Now you switch to another ink jet technology where the heads need to be replaced and require calibration for consistent output over time, you need that Spectrophotometer and calibration.