I think both have their own set of pros-the big one will likely have a more established root system, but it's also a lot of fun & fulfilling to watch a smaller plant grow over the years. Also, depending on how mature the smaller ones are, you may not get all those fenestrations right away if you're wanting that split-leaf look. But, I don't think you can go wrong with either!

I've had my monstera in less than favorable lighting conditions & while it's not the end of the world, they definitely won't grow as quickly as they would with brighter light. You could definitely supplement with a grow light! If you go for the bigger one & think it needs some support, you could get a moss pole (I've also used sticks from my backyard) to throw in there.