Best what? Price, capacity, life span, ease of maintenance, availability?
You don't want gell.
I have installed hundreds of deep cycle batteries over the years in off grid and back-up power applications. The vast majority are Deka. They have given me great service. There are just a few actual battery manufacturers. Everyone else just relabels batteries from these few companies.
Deka, Trojan, and Lifeline would be my top choices.