I have & love both ... In fact i hv the silver and onyx 8mm and then 4 of the mini bead bracelets (2 silver, 1 onyx, 1 amazonite).
I wear the mini's more bcuz I can stack them. I pair them w/ Alex & Ani for example or other T&Co bracelet styles. They feel very casual. I wear them w/ just about anything & anywhere.
But I dont love the 8 mm any less, they just feel a bit dressier and I am a stay at home Mom. But i try to wear them anytime I can if I do dress a little up for dinner out or something... They look great on their own. VERY classy. While the mini, to me, is very cute.
I think u should hv whichever u think ull wear more... Maybe keep what u hv and save up for the 8mm too. Then u can switch them out or heck, wear them together!