I did both! I booked my 2nd year accom in October in my 1st year with some friends I met that offered - which in hindsight I got pretty lucky with. We lived together pretty okay with only a couple of major problems (mostly one of my housemates continually having her much older boyfriend round..)
And then I went on placement, so I ending up sorting my final year accommodation really late (around June) and living with a group of 3 who needed a last person to make up numbers for their house. And had about the same experience - was generally fine but we still had some issues (messy common areas, people being loud in the night).
So in all honesty i'm not that convinced it makes much odds! If you're more academic focused (which I was) and you'll be out most of the day anyway studying/working etc. It really doesn't matter all that much. There's often some "artificial scarcity" that goes around with people being like "Oooh if you leave it too late there's no good houses left..." like, yeah, to some extent that's true but also no student houses are that nice. You will basically always be able to find somewhere, so I wouldn't worry about locking in that early.