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.
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