Lv 1 buildings will give the best return for all lands except lowlands (can build to l4) and hoarfrost (can build to l5 before return rate starts going down). Anything beyond l1 (or l4/l5 for ll/hf) will steadily return less gold per token, but higher levels make it take MUCH less time to liquidate tokens. So really it comes down to a balance between maximizing gold return based on how long you're willing to spend converting tokens.
If you want actual rates, check the guide "Guide to Crest Plate Use." The gold/token values correspond with how much gold you'll get back (higher gold/token value for a building level equals more gold per token you get back for tearing down).