Whatever gets you the needed materials or rank up gems for R3. I can't see the Paragon deals, so I can't give any specific direction, but if you need R3 champs then go for R3 materials.
As a Paragon, from what's available for Thronebreakers and Paragons...
From the Hunter's Market, if you can drop 9000 units you can get 2x t4a. If you can get up to 20000 you can get 7* 2-3 gems.
If you're paying, then you're probably looking at BP or Odins.
Short answer is - unless you are going to cough up the cash or pile in with a load of units, you won't get much rank up materials. Some, but not a great deal.
Comments
From the Hunter's Market, if you can drop 9000 units you can get 2x t4a. If you can get up to 20000 you can get 7* 2-3 gems.
If you're paying, then you're probably looking at BP or Odins.
Short answer is - unless you are going to cough up the cash or pile in with a load of units, you won't get much rank up materials. Some, but not a great deal.