Seaquest makes great BCs. I never tried the Black Diamond, but I have Seaquest Balance and assume they are very similar except the bladder size and # of D rings.
Balance had been great. It has the most comfortable pads that I could wear the BC on direct skin, no problem. I just cannot say anything bad about Balance except the small issue with the sure lock weight system.
However, recently my buddy was talking about Zeagle how good they are. I was curious and wanted to try, so I purchased Zeagle Brigade because Larry over at ScubaToys gave me a great deal on Brigade. Although I love Balance, now it is being sold on ebay. I thought I would never sell my Balance. Brigade is just superior. Here is why.
1. Brigade is lighter and I could take off 2lb of weight
2. Brigade is modular. If I need a bigger bladder, I can upgrade. Balance cannot.
3. I believe Sequest has some great warranty, but Zeagle has even better life time warranty I heard
4. I like the rip cord weight system better. I do not think I will drop my weights accidentally with the Zeagle system, but the weights on the Balance (the sure lock system) slipped out a couple of time. I guess this would be the only complaint I have for Balance
5. Brigade is based on Zeagle Ranger BC. The harness is rock solid. Although Balance has some nice D rings, Brigade has more of the tech D rings.
6. I believe Black Diamond and Balance are a lot pricier than Brigade.
7. Balance seems more comfortable on land. In water, it does not matter. Brigade is as comfortable as Balance
Balance has thicker bladder material and dual air dump on shoulder is nice. They are both excellent BCs, but I have chosen Brigade for the modular system.