Hey there
I've spent many hours contemplating your exact question and here is what my 2 cents worth is.
You can see my trip report of Mimpi indah here
http://www.scubaboard.com/forums/indonesia/359778-mimpi-indah-resort-bangka-island-trip-report.html
Looking at the pics on the net from the other resort Mimpi seems to have the best bungalows (on Bangka Island). The only issue I actually have with the resort (and it's not something they can do anything about really) is that they dont have a decent beach, but I would recommend them whole heartedly.
My take on the other resorts (all assumption made from their websites & reviews from tripadvisor and here on SB).
Gangga Island: Luxury!! Beyond my budget, but looks incredible!!
Nomad: Brand new and learning the ropes. Seems fairly rustic.
Coral eye: Seems pretty budget and rooms are all under one big roof, so not sure how "private" you will be.
Murex: Great location, beach looks amazing, but I've read so-so reviews about food and that the resort needs some TLC, it seems bit on the budget side, without the budget price.
Blue Bay Divers: They have their own little island with a beautiful beach and right in front of Sahung (not that the other resorts are very far from Sahung), the huts look comfortable and the reviews in general are all pretty positive. The only negative is that they apparently only have a brakish water bore hole on the island so water is scarce, so they dont have proper showers, you use what is called a mandi, or bucket to pour water over yourself, sounds primitive but you get used to it quickly and is part of the fun. For drinking water they get bottled water shipped in.
As I said above I've been wrestling with the same question because we are going to Bangka in July and my decision is to stay at Blue Bay Divers in July. The reason why is that we are taking a non-diver and she needs a beach to laze on while we are diving. And we wanted to try somewhere new.
Bangka is great and I'm sure you will have a great trip where ever you stay.