In terms of efficiency/speed for dapp usage, what light wallets are the best for dapp usage? Is there any notable difference between them? For example, what's the difference in speed/efficiency of Lace versus Nami?
wallet speed and efficiency depend by how fast they can submit your transaction to the network.
For wallets like lace, eternl, nami this is done by a service they rely on.
as an example nami relies on blockfrost servers to submit transactions.
eternl instead has their own servers so that they can better balance the load of requests.
In general the less people use the same server, the faster their transaction will be submitted.
The most efficient way to have a transaction submitted is by sending them to a (trusted) stake pool node, since those are the nodes that ultimately will execute the transactions.
the above doesn't necessarily have to be a full wallet (like daedalus to be clear); you can just have a full node somewhere in the world and then submit your transaction there using the cardano-submit-api.
some stake pools are exposing an endpoint where they accept transactions for you to send.
So if you want your transactions to be submitted efficiently you might want to consider setting up a node on your own and then use any light wallet by specifying that you want to use your node (instead of their default servers) in order to submit transactions.