My first piece of advice would be to just not and find a different flight. As others have noted, the 739 is the worst plane in the domestic fleet with the exception of the original CRJ. Everything is cramped, poorly thought out, and uncomfortable including F. I personally will not fly on these, not even from MCO to ATL and will book at a different time or elsewhere if I have no other option.

With that said, I'm not much a fan of the bulkhead but if you're looking for three seats together, they options are all pretty much equally bad. The only tolerable seats are 21A/F but that's not very useful for 3 together. The best advice I can offer would be to find a 757 or A321.