I've fished them both and both are rewarding to fish. I think Hartwell is an easier lake to fish, in fact much easier at times. Jocassee probably isn't, but it's considered a trophy lake, has trout in it and is truly one of the prettiest lakes on the planet, so well worth fishing, at least once. I'm not trying to discourage you from fishing Keowee at all because I like Keowee a lot (landed here as a retirement location for a reason), just pointing out that there are lots of other options, although you're right, some of them involve a drive. My situation when I'm up north is that the nearest lake to my home (at least the nearest lake that's even worth considering) is an hour away and the nearest "good lake" is 1.5-2 hours away, BUT, within 3 hours I have a LOT of really good options and a little bit further than that and there are a few more really, really great options as well. To me, being down here and having 3 good lakes all within 30 minutes or so is just unbelievable.
I should also mention that I don't think Keowee is quite as tough as some people claim. I almost never get blanked on the lake and I have enough really, really good days to prevent any real frustration when you do have the tough ones. And, I live and fish here during the wintertime which many people would consider to be the toughest time to catch them. Fortunately I'm also here in the springtime when it can be fairly easy.
I'm taking two buddies out on Thursday and given that they don't fish a lot from a boat (almost never, they're almost exclusively fly fishermen), I'd really like them to catch some fish. I also think that they'd like to take some home and given that Spotted bass are invasives here and the DNR encourages you to harvest them, I don't have a problem with that. They want to fish for Crappie and Spots and I'm going to go out this morning and do some scouting and pre-fishing for them, so hopefully it's rewarding today too.