I rocked an Alembic for several years and I’ve owned Bag End and currently own an SWR cab. I was (and am) very happy about my experiences with both. I’ve also got a lot of experience with various Mesa amps and cabs. And I really liked those too.
If I were shopping for a new cab right now I’d definitely consider Mesa as my first choice out of the three you’re looking at. Because while
all three will deliver a great bass sound, Mesa has the advantages of: (a) still being in production unlike SWR; and (b) being known and more popular than Bag End - which means a higher resale value if you ever decide you want to get something else someday. Mesa’s service is also the best out there IMO.
So unless you want to take a chance on an orphan amp/cab line (with the original speakers since IMO it was the now long discontinued PAS drivers that set the Goliath series cabs apart) I’d probably avoid SWR unless you really want one and can get a good deal in it.
Still, as others suggested, if you still like what you currently have - and don’t have a clear idea of what you may want to migrate to - you’re probably better off holding off on buying something else for the time being. “Bird in the hand” as the saying goes
n’est-ce pas? 