Get the best you can afford.....min 5 inch.....I'd suggest the 7" models. The HDS 7 touch has treated me great for almost two years now. If you can't keep from dunking your ff when you come in...then get the warranty.
Once you have your FF.....put the manual next to the toilet and let that be your reading material for a week or so.
Not too many know how to properly set up their FF, it's fun watching people drop irons in the kelp thinking it's a monster school of yellows.......
but I think I find myself doing the same from time to time..