Hi Big Tuna,
The 2 most frequently mentioned operations are "Blue Water Divers",
and "Dive Bermuda".
Both have gotten good endorsements from people on SB.
I have frequently dove with Dive Bermuda, and have had excellent experiences with them.
One thing to note:"Getting around" in Bermuda with a set of dive gear can be tricky and expensive- so where you are staying ( how far from each dive shop) might be an important consideration.
If you do a "search", I'm sure you'll find a number of recent detailed threads on this topic.
I have heard of Triangle divers, but only the name.
Don't forget that water temps in Bermuda in April will not be as warm as in the Caribbean, so you might need more in the way of an exposure suit.
Good luck,
Mike