Once you decide on a battery size, you will want to think about what kind of batteries to buy. The biggest decision is battery technology. While things like lithium ion are really cool, they're still an emerging technology that is kind of expensive for what you get. For most of us, the action will be in batteries with lead and acid of some kind. The three basic types of lead acid batteries are wet cells (flooded lead acid), absorbed glass mat ("AGM") and gel. For whatever reason, the gels haven't really taken off as deep cycle storage batteries. My guess is that most deep cycle storage users that are interested in a sealed battery move to AGMs since they are a little more rugged than gel. So most of us don't really consider gels for house batteries.
AGMs are expensive. Usually, you will spend at least double the cost of a comparably-sized flooded lead acid to get AGM. To make matters worse for AGMs, the absorbed mats don't make power as readily available as a wet cell, which means that a same size AGM will have only 80% or 90% of the Amp-hour rating of a flooded lead acid.
Since AGMs cost more and deliver less, you would think they would be the dumbest thing in the world to buy, right? Probably, but I can think of at least two reasons why smart people buy them anyway. First is a safety reason. Flooded lead acid batteries give off gasses during normal operation. That gas contains hydrogen. As the passengers of the Hindenburg would tell us if they hadn't died in a ball of fire, hydrogen gas is flammable and dangerous. The sulfuric acid in batteries adds some other chemicals to the mix and make it not healthy to be around. AGMs don't off-gas during normal operation. If your batteries are inside your cabin or any enclosed space, you pay the money for AGMs and don't look back.
Another reason to buy AGMs is a "know thyself" proposition. If you are the kind of boater (or have an owner in your houseboat group) who you know will let flooded lead acid batteries run dry, you are a good candidate for AGMs. Since you never have to add water to AGMs, you can't cause them to suffer a premature death from going dry. If going dry is likely to kill your batteries in less than half of their normal life, paying double the price and getting AGMs puts you money ahead.
Since you got five years' life out of your last set of flooded batteries, you are still ahead of the game. Five years is more than half the life I would expect from a fancy set of AGM batteries. For your situation, I would roll the dice on another set of flooded lead acid wet batteries and promise myself that I will take a bottle of distilled water to the houseboat and use it from time to time.
There is still a little to consider, but this post is getting long. I will try to add some more later when I have a minute.