agreed, and that's why I don't recommend anyone buying the first model year of anything. Seeing that this is just an update and not a completely new vehicle like the Navara or Hilux, I would think they've sorted out most of the initial kinks.
My little take on your choices:
BT-50: Don't care for the looks. If Mazda does the next gen or a even refresh in the style of the rest of it's current line up, it will be a thing of beauty. Parts shouldn't be an issue, but I'm still iffy of SS's service.
New Frontier 4x4 manual: Can you get this with those "NASA inspired" seats? Sat in a fully loaded automatic one a while back and it was easily the most comfortable local truck I've been in. Does the manual come with leaf springs or coils?
Isuzu- Underrated brand in Trinidad. Comes across as the stepchild in SS's portfolio. Wouldn't bother with the smaller engine, but the larger engine does make more of a clatter than other trucks. Same comment as the Mazda parts and service goes here.
Hilux: front reminds me of those duck boats that can drive on land and directly into the water to do tours :/ and I wish the interior looked more cohesive. It is the newest of the bunch, and if you're looking at the 2.8L (non TTTL), that engine is yet to full prove itself with our fuel.