well, i'm going against the grain here. i use fabric conditioner in all my washes and always have done. my towels dry me and the rest of the family perfectly, no issues at all. i use whichever fabric conditioner is on offer in costco or failing that, aldi's own, or asda's own, whichever supermarket i happen to be in. there may be scientific evidence but in practice it makes little or no difference.
I think it depends on the fabric itself ..
I have some posh white ones stolen from Hilton Hotel (we won't go into that) and however I wash them (with or without Lenore Pure) they stay very 'full', absorbent and 'hard/scratchy' (which I like)