Just HD, some true widescreen support, and a touch of AA is good enough for me. So I'd probably say HD. As long as they don't cut corners in other areas, such as RE4HD's poor audio (which is not even in Stereo or ProLogic II). It is a shame that Capcom did that to RE4HD. They even removed a lot of sound effects and changed voices for some enemies that did not need to be messed with (see the Garrador's grunt when you shoot him in the back).
Eh... I guess I'd say a cross between an HD upgrade and a remaster is sufficient for me. Remakes are tough to get right without the original development team around to handle the project. Changing even the smallest detail "for the better" can greatly impact a game's overall atmosphere a lot of times for the worse. It's a huge risk.
Resident Evil 1 was remade with Shinji Mikami and co. on board. That is why it worked. Other full remakes haven't been as fortunate due to having a totally different team in charge of the remade version's production.