I like to fly the circuit as tight as possible - nice to be able to glide in if you lose power. I'm only low-hours but I admit to getting frustrated at these 'bl00dy learners' who fly huge circuits - I then remember that I was in that position not long ago and remember just how high the workload seems at first and chill out.
To be honest, I've never considered what height I should be turning final - it sort of comes by instinct - whatever seems right on the day. If you try to do it by the numbers it just wont seem 'natural'. You ought to proctice both scenarios with an instructor - coming in low on the wrong side of the drag curve and being way too high and slipping-in for the numbers. That way you'll cope whatever happens and wont let it worry you.
Chill out - if you're at a new field and there's somebody local in the circuit - follow their lead. If there's nobody else there, do it your way and nobody'll be affected if you get it a bit wrong. Once you've been to a couple of strange fields you'll wonder what you worried about.