Furcal is the ultimate headache this year. You simply cannot drop a guy with his proven talent, and the SB's have at least helped him maintain some value in spite of his horrendous BA. But this shoulder simply doesn't sem to be getting any better, and at this point, I'd be satisfied if he can pull himself up to .250 and swipe about 40.
Reyes is flat out overrated at this point. He's got huge upside, but right now he's an average guy who is overvalued by many fantasy owners.
Hall is a major surprise. I didn't see him as much more than a utility guy at the big league level, but he apparently figured something out over the winter.
As for Lopez, hey, the guy can hit. I believe he will eventually settle in the .270's someplace, but with 20 HR and a handful of SB's, that's not bad at all, especially for a guy who wasn't drafted in any leagues.
Rating them is pretty tough, and I believe it might depend on whwre your team stands. Obviously, Furcal is the clear choice on career numbers, but his health is not good, and he's risky for this season, IMO.
As goofy as it sounds, I would not be shocked if Lopez ends up as the highest rated player of this quartet for the season. But if I had to select one guy, I'd still go with Furcal as he has the biggest upside if he's sound. And despote his stellar showing to date, I'd still put Hall at the bottom of this short list.