The Tavern

Playing as a merfolk so in either case I can get mindelay quickly enough

I think that the answer is: the +1/+3 bonus is cumulative, the damage inflicted with weapon type is multiplicative, so the halberd is better in the long run, if you don't want a shield. I never read the formulae on my own, however, so I'm going by hearsay with this one.

I'm a huuuuuuge fan of shields, so I would go with the +3 trident until I found a demontrident, then ride that out.

You're a merfolk, so like you said it's not a problem to get the higher skill. Unless you're already using a good shield, I'd use the halberd. Eventually you'll want a glaive, or demon trident and a shield.

As a merfolk, you can get away with a bardiche, but 26 skill is a lot, even with +4 apt.