There are far, far too many options to lay out a best case/worst case scenario here, so let's just dive into it.
First off, I wouldn't at all mind seeing what Xavier Nady can do with a full season at first base and an off season separated from shoulder surgery. Second, the only reason I would hate to see Adam Dunn playing there is because I would then have to root for him, and no longer call him a "big dumb animal". Third, Paul Konerko playing really well in a contract year is no surprise. Not ready to throw him a treasure chest just yet.
There are a lot of options available for first base this year. You will hear a lot of clamoring for Adam Dunn, whom fans either love or hate with nothing in between. Some will argue a pigeon will catch as many balls at first base as Dunn will, others will argue that while that may be so, the pigeon will not be able to fly farther then the balls leaving Dunn's bat day. after day after day. Dunn will also want a pile of money for a team that will be knocking at the door of fourth place next year - no thank you.
I would like to see Xavier Nady sign another similar contract to this years' $3.3ish and if so, then 1.5 good years of Nady for 7 million will be the best FA signing of Jim Hendry's career.
If Paul Konerko wants to be a veteran presence for a discounted price then he would be a find. If he wants to ask more than 10mil per for more than 3 years, he'll be joining his old buddy Jermaine of the gold course.
Given a choice between PK and Dunn for 10 mil, I'd have a tough time deciding, but I'd have to go with Dunn. Yikes.
All this is moot since we'll probably end up with Lyle Overbay for 16 years/227 million, but hey. That's Jimmy!