How would the most basic taproot transactions (not involving scripts) compare to P2WPKH transactions in terms of vbytes or fees?
Taproot inputs are smaller but outputs are larger. Specifically, P2WPKH (Native SegWit) inputs and outputs take 68 and 31 vbytes in a transaction, respectively, while P2TR (Taproot) inputs and outputs take 57.5 and 43 vbytes, respectively. In terms of fees this makes Taproot transactions about 1.5% more expensive when you don't use multisig or scripting.
2Note that the cost for the output is paid by the sender, but the recipient saves the cost on the smaller input; the recipient picks the address they'd like to get paid to, though. :)– Murch ♦Jun 21, 2021 at 2:47