I don't personally love eternity rings, so I would probably pick the bracelet. What would you wear more??
Actually my choice would be neither and I would opt for big, gorgeous studs! No piece of jewelry has made me happier in my "mom-life" than my earrings. I only wish they were bigger!
If you dont have a nice RHR that you already wear then I would pick the Eternity ring but I would make it only 2/3 or 3/4 and
leave room for sizing. If you already have a nice RHR then I would pick the tennis bracelet.
How about an eternity ring with colored stones....pink for a girl, blue for a boy. I have a friend who did this and it looks great with her wedding rings.
I just had a baby 5 months ago, I vote smooth prongless eternity. Any bracelet will quickly become a chew/pull toy. I wear my 5 ct asscher eternity daily, I just wish it didn't have prongs! I'll be resetting at some point down the road.