aidanhydro,
First of all what are you trying to do with this battery? Are you running an inverter with constant drain? So many questions! We need more info. Tell us what you are expecting the batteries to do.
I'm assuming you're using this in a renewable setting, putting something into the battery from somewhere amps wise, and drawing them (amps) as well.
Personally I would get the one big battery. Why? Cable and connectors alone becomes an issue with a bunch of batteries. More points of possible failure=more failures. I know, I have 12 6V flodded golf carts, and wish I had 24. I still have to keep an eye on all those points of failure.
If you're only gonna have 100 amp hrs I assume this isn't really a mission critical battery/power system. 100 amps may sound like a lot but it really isn't. Used very wisely it still ain't a lot of juice.
I say keep it simple, but remember that normally in an off-grid or heavily depended upon system, the battery is going to get a workout. Period! If this battery is going to be a standby, one getting a charge when it isn't used, it won't be as bad or if you don't cycle it too deeply or for too long. Low voltage states for extended periods of time are mortal enemies of the common flooded battery. Never let a flooded bat stil drained any longer than you have to.
Bigger batteries are like bigger aquariums. If the chemistry gets off a little the sheer volume of liquid dilutes the error. On the con side it takes more effort to equalize, if you don't run a desulphator. Also usually a large flooded bat will use proportionally more water by increased surface area vs a group of smaller bats. Bigger batteries usually have more space and or cell division material than small batteries. Short-out issues are reduced in bigger batteries, and the "dregs" that fall from plates has a deeper resevoir. Kepping that sludge away from the plates is good.
Bigger batteries have less sensitivity to thermal changes. Just like big dinosaurs were less responsive to change in temperature, big batteries take longer to heat up or cool down. Rapid temperature changes are not good for normal batteries, but I hear gels are less susucptable. We know the dinosaurs went the way of the 10 year old "Die-Hard", but it wasn't because of rapid temperature shock. All this is irrelavent if one protects those batteries from the elements to begin with.
If your charging system(s) goes down the bigger your battery bank (not size physical, real amp hrs) is all you'll care about. So however you choose, for whatever you're doing, I'd go with as many, and as well made, true deep cycle batteries as I could afford. In my mind the battery bank is the guts of the system. I'd also go with a big meaty battery, just 'cause they can take some abuse. Not that I wouldn't love to have 6 new glass jar 2V batteries like we saw here recently or anything.
uuuuummmmmm glass jar batteries..... uuuuuummmmmmm ( drool puddling on desktop ;~Ô ).
RogerAS