Please don't go by a quote by me. There is no real spec when you are talking about house batteries or even cranking batteries with waverunner engines. The spec you are looking for is so small, that you will have a tough time finding a battery that doesn't meet this spec.
The house battery is as big as you have space for. The group is literally the physical dimensions. So when you have a boat with a battery box, or tray, you literally put in the biggest battery that will fit in the tray or your wallet. As that is the whole point of a dual battery system is to isolate the engines from the other crap in your boat. I chose Group 27's as they were the largest I could fit in my tray when i replaced them. (BTW, they were Duracell's from Sams Club in 2018, so your a right to avoid them, their life is pretty short, smile)
And also to provide as much duration out of the batteries, not cold cranking or marine cranking amps. Your stereo equipment will want a minimum voltage to operate, that's it. So researching for a certain marine cranking amps is irrelevant. As far as the motors, they will have a minimum spec, but any full sized 12v battery will turn them over, as that amount is tiny. Have you seen a waverunner battery? The batteries in my pair of waverunners are smaller than the one used in my lawn mower! So any single 12v will turn them over.
The kicker is getting something that will last for the way you use them, and each owner is different. Some don't have access to power, so they need them to recover quickly with the small amount of current coming from the stators. Others, want longer run time, but have access to power, so their onboard charger can charge them overnight. So they want duty cycles. This is the difference between deep cycle, cranking, etc, etc.
So back to brand. HangOutdoors probably has the most experience on here with very expensive batteries. I'm sure he can chime in if you want to drop a ton of cash on batteries. But he had a very specific purpose above and beyond 1000w stereos. So your mileage will vary from his experience. And like everyone else, we all have our own experience.
Brand is not as big of a deal for the load we are putting on these. As mentioned above, I put two Duracell Group 27's in my boat, and two of the same on my Floe Lift in 2018. All four are plugging along. The two in my lift have not been charged since I dropped in in the water after ice out this spring. The two in the boat get a full charge with my onboard charger in the boat every other week. I don't think they owe me anything, as I think I paid $80 each at Sams. BTW, they sit in my boat from October - May in the MN cold with no trickle.
Good luck,