I have both a Surly LHT and a Salsa Casseroll. If you're looking to do brevets / fitness riding as opposed to touring / utility riding with loads, the Salsa wins hands down. Forgive the lack of technical terms, but the Casseroll feels much livelier and handles bumps and road vibrations better. Some of this can of course be explained by how they're built-up, but even when I've ridden the LHT stripped as light and bare as possible it isn't as "fun" to ride as the Casseroll. Not to mention that the "ginger beer" paint job is dead sexy.
They're both more than capable, but if the Salsa is within your price range I couldn't recommend it highly enough.
One gripe that I have is that both of my bikes have Salsa Delgado rims and I'm honestly disappointed with them. The rear on the LHT (36h, max of rider + gear at 250lbs with some touring) cracked at several eyelets and I replaced it at 5000mi. Just yesterday I noticed some small hairlines (but can't yet catch a fingernail on them) on the Casseroll's rear (32h, never seen more than 200lbs or super-rough riding) at 1600mi. Certainly not disastrous performance, but I was hoping for much better.