Hi
I'm sure every child is different, but from what I've read they don't really benefit from social interaction until 2 or so.
If you have the option, I would say go with the family member if you can - the main reason being that, based on our experience, your DS will probably be sick, sick, sick from being at daycare

DS started at about 16 months, 2 days a weeks. In the first 5 weeks he missed half the days due to illness. He then did 4 weeks in a row and finally settled in (not crying when I dropped him off anymore and starting to smile and talk to the carers). He's off sick again this week

I think at this age most kids are upset when they first start, but will settle in once they get used to it. DS does have fun playing there.
It has defnitely caused a spike in speparation anxiety - he has taken to cuddling a special toy all the time. He never did this before. This has also upset his sleep a lot, as he doesn't want to be left alone at night. It's particularly bad on daycare nights. This too is easing up now, though, as he's getting used to going.

I should add - my negative opinion is very much biased by the mummy guilt I feel at sending DS to daycare....