IMO, hydraulic. Also, now would be a good time to do the "Big 3", in addition to chasing down any grounds and cleaning/replacing them. Other things you might do, not related to the engine bay, include silicone lubricant on the windows. This will make them raise/lower more smoothly, and use less power. Replacing the intermediate shaft bearing (don't quote me on that!) that makes for a smoother steering experience. Examine all the belts and belt tensioners -- replace any suspect ones. If you haven't recently replaced the radiator, flushing the radiator might be a good idea. Fuel lines, evap lines, etc. Check and replace the spare. Clean all lights if they are all foggy. Check your suspension components for play, replace as necessary. Now would be a good time for a big brake upgrade, and/or a hydro boost conversion...
That's all I can think of at the moment. I mean, if you really want to go crazy, you can replace all the blend doors.