As a veteran of many many leisure batteries over many years in the last few months I've taken a punt on a cheapie.
The best battery in my eyes.
The best battery to get? The one with the biggest ah from a scrappy. £10. If you're trickle charging.
Leisure battery-one with the longest warranty. Not had one last more than 18 months.
AGM-no, not at all. They are really designed for stop/start technology.
They are very expensive too. (£500+, not uncommon from a dealer)
Think how many 'regular' batteries you could buy with that!
11 years I've been WFP. And now, I wouldn't buy anything other than a £10 scrap merchant special.