Civ IV, IMO, is one of the best strategy games of all time, one of my favorites for sure, and the best of the civ series (til 5 hits and blows it away).
That said, due to my love of fantasy, there are times when I've considered FfH to be better than civ itself. It's truly an amazing thing how the FfH team transformed civ for fantasy purposes. Everything about it feels right even with it being built on civ. The races are all incredibly diverse and well done, the magic system works out great, the violence of the world is great. Monster lairs and dungeons/goodie huts are all well represented and make sense. It's just a wickedly good thing (and there's little wonder that it got scooped up to become a stand-alone game that's in production). It also has some MoM-like feel with how the magic nodes work (and other stuff). And you still have fantasy themed wonders. In a lot of ways it's like the best of many things combined - civ and DnD with some MoM influence - sexy. (FfH is based on the lead designer's old pnp DnD campaign).
So, ouch, really tough call.
I love FfH and still play it (and regular Civ IV:BTS, just as I still love to play GC2).
Elemental is kind of in a rough state and it'll probably be a few weeks/months before it's truly in a state it should've been in for release. Elemental definitely has good parts about it now, and a lot of potential, and it's playable/enjoyable now. A lot of Elemental's mechanics are different and cool (like city expansion, for ex).
My biggest problem with Elemental now is all the lockups and crashes - it's really, really irritating and pretty much unaccpetable in a modern game. How many times has Civ IV:BTS or FfH crashed on me? I'm sure it's happened but not enough that I actually remember. Elemental crashes or locks up so much that I set autosave to every turn because I know I'll be restarting the game and loading a lot. Arg!
I can't realy recommend one vs the other, but I will say that if you own Civ IV, like fantasy (you're here aren't you), and have not checked out FfH, that you have failed. FfH is amazing and absolutely worth experiencing.
I generally don't screw with mods for games like this or civ, but FfH isn't a mod - it's a total conversion of the game - it's like a seperate game - and it is incredibly well done.