Both will give your VPS a "home" IPv6 address, but if you also expect to receive an IPv6 prefix/subnet, DO only gives you a /125 per VPS (8 IPs). I moved my VPN nodes to Vultr for that reason; they give you a /112 (65K IPs) per VPS.

Neither DO nor Vultr actually routes the assigned prefix to your VPS, so you have to run something like ndppd [1] to answer NDP queries for IPs in the IPv6 prefix you've been assigned if you want the local router to send your VPS any traffic on those addresses.

[1] https://github.com/DanielAdolfsson/ndppd