Personally i used to go for first of the day , and generally had good experiences, i noticed being second does not matter that much either. I always avoided being last mostly because back then shift would finish late (2 am or such) and i didn't want somebody drunk or exhausted. But with girls working noon to 6/8 and such, i feel more "safe" if im to be last of the day especially a well reviewed provider.
Also some services are usually more prone to happen on last shift (cof for instance). But if you are last there always a chance that hygiene will not be at its peak, not nessessarely the girls fault but if she see 6 guys, after a while its natural it could happen. I mean if you masturbate 6 times in a few hours in a day, pretty sure your dick will get sore too.
Anyway nowadays i just try to not fuzz about it. I prefer a booking before 8 for convenience no matter if its the beginning or end of her shift, and 10pm will be my absolute last call personally, but i don't really take too much of a look where im gonna be positioned. I tend to see well reviewed, reputed providers more these days tough.