Orlando because they have an extremely talented backup center in Marcin Gortat who can fill part of that void left by Howard.
A three man wing rotation of LeBron, Vince and Pietrus. Jameer at the point. Anderson, Bass and Lewis sharing the remaining frontcourt minutes. Need to sign either a backup guard or a backup center in free agency.
Lots of lineup flexibility with LeBron's ability to play four positions and with Rashard Lewis as a combo forward as well as big wings (Pietrus, Vince) who can man either wing position ...
A big lineup with Bron at the point, Vince at the two, Shard at the three, Gortat at the five and either Bass or Anderson at the four. That would be fun to see. You could even use that as a starting lineup and have Jameer in that sixth man role that he plays ever so well.
Or a lineup where LeBron plays the point, Vince and Pietrus on the wings with Shard and Gortat up front. Then sign an MLE player on the wing in free agency (say Mike Miller) and have a bench of Nelson, MLE wing, Ryan Anderson and Bass.
I love that versatility, that lineup flexibility.
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Cleveland would need significant reconstruction. Mo Williams isn't able to be a starting point guard in this league without having a teammate or offensive system that can take some of the playmaking responsibilities off of his shoulders.
Jamison can work for the time-being but due to his age will need to go. Varejao is still great for that sixth man role. No talent on the wings. Delonte is a useful backup guard. Hickson is a decent piece but his minutes will be limited by Jamison/Howard/Varejao.
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I think Orlando would become the best team in the East.
As for Cleveland, I think they would be in the Hawks realm of the world.