
All three rounds: DSA, LLD and HLD. Same sessions as the individual ones, cheaper together.
Worth doing as a set because I see all three of your rounds, so at the end I can tell you which one is actually holding you back. That's hard to work out from one mock.
Space them out over a few weeks so you have time to act on the feedback between them. Valid for 3 months.
Start wherever you like. Most people start with the round they've done least of.
Between sessions, askmaddyy.com has my writeups on system design and CS fundamentals, with interactive demos.