I’ve played all of them, and while 3 has a special place in my heart I’m going to have to agree with the crowd and say 11 is the best. If you need convincing, watch the Tim Rogers kotaku reviews

VIII is the best one imo

3, theres a remake out soon

All the DS Dragon Quest games are perfect imo - V especially. IV and VI are also really good. V was my first entry, back on the DS. IX is probably the one that has aged the worst, because it had really nice online co-op on the DS and with the servers now defunct - you’ll miss out on that feature entirely.

XI is a fine modern jumping in point if you’re unfamiliar with the series and aren’t a huge RPG fan.

Gonna throw in another vote for 11, it’s the only one I played all the way through besides 9 and I think I only finished 9 because of the wacky class system