I prefer Al Horford over Al Jefferson or Dwight Howard.
This. Horford is the jack of all trades that I think would help the most out of the three. I predict there will be some serious talks between the Hawks and the Celtics before the deadline.
i would prefer Dwight over Horford.
Dwight has declined over the years, but he's still putting up very impressive numbers and still has the ability to be dominant on defense and on the boards, and even occasionally on offense.
Horford has also declined over the last few years, but he's putting up only mildly impressive numbers this year, and is really only 'good' as a rebounder, defender and scorer. Like Dwight, he's also very injury prone.
IMHO Dwight is the bigger impact player - he has the potential to be an absolute game changer in the playoffs because even in his current (declined) state, he still has the ability to completely control the paint.
Horford on the other hand is kinda like a rich man's Kelly Olynyk in that there isn't any one thing that he is really dominant at, but he'll just make your team better by quietly doing a lot of things well.
Given the choice, I'll take the guy who has the potential to dominate. Teams with lots of solid guys but no dominant ones usually do very well in the regular season, and drop off the face of the earth come playoff time - Atlanta being the perfect example. Teams with guys who can dominant certain aspects of the game tend to be the kind of teams that make hard runs in the Playoffs.
With Thomas dominating on offense and Dwight dominating the paint, I think that this team could be really deadly - and a front court duo of Olynyk+Dwight honestly feels like a match made in heaven.