I'm going to assume this is a long term keeper league, and absent you telling any of us any information on how your league works, I'm guessing you get to keep these guys indefinitely. Second, I'm an owner of Maybin, Buchholz and Porcello, so I'm not favoring one or the other because of personal attachment. I'm also guessing that David Price is not available for whatever reason that doesn't make much sense if Weiters is.
There are a couple of reasons why Maybin should not be #1 on this list. First off, he's most likely getting a starting job this year, 2 years too soon. He'll likely slump (he strikes out, A LOT), like Homer Bailey did last year, and his cost will plummet. You will be able to trade for him for much cheaper of a relative value than picking him overall first in this draft. Why will he slump? He was below par in the AFL, and his bat was exposed during his call-up with the Tigers this year.
As a 20 year-old, he started the year in High-A Lakeland, and displayed everything but good plate presence in terms of pitch recognition and long swing. He was striking out 23.8% of the time versus walking 12.3%. Now, those were small improvements based upon his first year in A-Ball, however, he was still striking out nearly double the amount of times he was walking. Considering he was 20, that's not bad, but it's also not great, especially if you are going to rush him. That presence gets exposed against older pitchers who have the ability to throw pitches that he cannot hit or hold off of more successfully.
His promotion to Double-A Erie lasted a whopping 26 Plate appearances before his promotion to the big club, which is rather unheard of. Players do get promoted from AA all the time, but not after only their first few games there. His sample size is so small that we cannot discern much from it, other than he made much better contact, was much more patient, but hit without any real power (only 1XBH).
It goes without saying that his shoulder injury had a large impact on his showing in Detroit and the AFL, but it should not blind one to the fact that his bat simply was not ready. He likely needs a full season in AA before he gets a call, but unfortunately in Florida, they need a CF. Whether or not this sets Cameron back remains to be seen, but stinking it up royally tends to have a negative impact on the progression of prospects, and one fears this outcome for Maybin coming off two bad previous showings. The conservative estimate says that Maybin is due for a promotion to full time mid 2009. And this is why he should not be #1 on this list.
Who should be? Clay Buchholz. Say what you want about the shoulder issue at the end of last year, but that was a product of him being at his protected inning limit rather than any structural issue - Buchholz has one of the best repeatable and smooth deliveries in the Minors, and worrying about any health issues when there really have been none is foolhardy. Conversely, I also think that you should not put a ton of stock into the no-hitter. We all remember Jered Weaver and Zack Duke's entry into the Majors, and this was likely partly a product of the other team having little information on Clay. But it would also be foolhardy to assume the same outcome as Weaver or Duke. Buchholz is SPECIAL. He has THREE (one fastball, 2 offspeed) plus pitches as well as PLUS command. That just doesn't really happen. The make-up is there to be a TRUE ACE. His Dominance rates were in the TWELVES in the Minors, and he hovered around nine in the Majors. And when you consider he'll pitch at the back-end of the rotation for the World Series champs, his ability to get you a lot of wins and a lot of strikeouts with great percentages, THIS YEAR makes him the unequivocal first overall pick. His relative value after the draft is only going to go up. And his long term potential matches that of Maybin.
The list would be as follows, with an * denoting players who will have a positive impact this season:
Fukudome* (his long term is not as bright as the rest of these players, however, he'll have impact immediately)
Price* (sure he's not available?)
Joba* (injury history puts him below Maybin)
The rest are FAR AWAY from making the bigs.