Here's the thing...
If you are REALLY interested in doing match shooting that requires you to use sling pressure for max accuracy, then neither barrel is good enough. You'd want a MATCH barrel and a float tube.
The ONLY advantage an non-match HBAR has is doing extended full-auto, which is why the SAW has a heavy barrel. Note that the M16A2, and even the full-auto M16A3, use the "A2-profile" barrel. Unless you plan to use your AR as a back-up boat anchor, get the A2!
The AR manufacturers have convinced (almost) everyone that HBARs are better, when all they are is heavier and cheaper to produce.
Again, if you're looking for a benchrest/match/varmint rifle that will spend its life on a bench, then you DO want a (free-floated, made from a match-quality barrel blank) heavy barrel. But if that's what you wanted, you'd know the answer to your question already.
-Troy