Ubisoft store is having 20% off everything with the code EXTRA20
Here are the different editions on sale:
Rainbow Six Siege Gold edition [ubi.com]
: $19.80 after coupon, includes 8 Year 1 Operators + 8 Year 4 Operators + 600 in game credits and some skins
Rainbowsix Siege Deluxe Edition [ubi.com]
: $7.92 after coupon, includes 8 Year 1 Operators only.
Rainbow Six Siege Standard Edition: $6.4 After coupon, includes no operators
Rainbow Six Siege Ultimate Edition [ubi.com]
: $32 after coupon, includes all legacy operators, year 1234 operators, 600 in game credits, and some skins.
Rainbow Six Siege Year 4 Pass [ubi.com]
: $14.4 after coupon, Requires the base game, includes Year 4 Operators, 600 in game credits, and some skins.
If you already have the base game, you can buy the Deluxe, Gold, Ultimate, or the Year 4 Pass and essentially unlock all the content from those versions.
If you are just starting, I would recommend the Gold or Deluxe editions. If money is not a problem, get the Ultimate. If you want the cheapest version, the standard edition is not worth it for $6.4, get the Deluxe for $7.92 instead.