However, with chip transactions there are multiple calls for different payment processing flows. For example, a transaction could require 5 round trip request responses from the chip to the payment process meaning 5x the time required.
Samsung pay even cuts out any knowledge of the reader, just gives a virtual number to the credit card mag reader.
The main practical difference is that you can't update the on-card data depending on the transaction outcome, since the card isn't there any more.
Paying for the bus for me is offline, whereas in a supermarket it's processed online
The other kind, AIUI, are indeed the same as the chip transactions, with all that entails.
e: Other posts seem to say that all the contactless transactions are offline, which means no multiple expensive round trips upstream either way, so nevermind.
IIRC it should come down to 0 or 1 roundtrips, depending on the amount and risk profile - in most cases you do an offline authorization where only the chip is involved to verify the txn, PIN(if applicable) and limits; and if you can't do that, then you send an online authorization, get a response, and that's it. There's extra communication afterwards in the workflow, but that happens after the customer has left and has no impact on customer-observed latency.