I say "like to run" as a I'm quite keen to do the research and prep work. I'd be equally happy to play any of them too.
I played a fair bit of MERP in my youth, but I'd like to try to re-visit Middle Earth with a more appropriate rule set and my now much greater appreciation for the setting. In what little spare time I have at the moment I'm laying some groundwork for a campaign (although I don't currently have a gaming group!) and as part of this have just re-read the last few chapters of Lord of the Rings on my way to the appendicies. It struck me how morally black and white the book is (although some of the history less so, e.g. relations between the Rohirrim and Dunlendings, where the "good guys" can't really claim any moral high ground) which will be a challenge. I'm used to characters being a lot more ambiguous... I'm getting more and more interested in The One Ring as a system, which amongst other things seems to have some quite flavourful mechanics to address the Shadow that hangs over Middle Earth.
Norse / Celtic / Sidhe
A mashup of Tad Williams' Norns and Hernystiri and C.J. Cherryh's The Dreaming Tree, with a smattering of the Bloody Nine. Castles & Crusades Codex Celtarum is looking quite interesting too.
Original Enemy Within campaign - Warhammer FRP (1st edition)
I've never run the original Enemy Within campaign which is a bit of an oversight, given that when I was actively playing WFRP was my preferred system.
I first heard of Empire of the Petal Throne in my teens, and thought it sounded cool, but never discovered anything about it. Now I know somewhat more I'd be interested in running a campaign to move me a bit away from my northern European default.
I originally dropped BECMI D&D for WFRP, through a mix of Games Workshop marketing and loss of faith with D&D and PC power levels in particular. Nowadays I think I'd cap things at level 14, or perhaps even try E6. However it'd be fun to try a stereotypical high fantasy campaign, applying everything I've learned since I last ran D&D.