McC and Upton are about the same in terms of power numbers. McC will always have a better AVG., but not as high as right now. Upton will give you more steals. IMO, AVG is harder to find than SB. So, McC gets the nod.
Davis is a guy who should get you: 4.00ish ERA, 1.3 WHIP, 13 wins and 7.5 k/9. That's pretty good for a #3 start, like you said. But remember he's only 24 years old an could get a lot better in a year or 2.
When you add it up, the deal is pretty fair. But you get to keep a guy for $5 who is worth about $20. I'd take it. You can always fill in a SP or 2 off the WW.