We use iZettle.
Works really well, and for most customers its a bit of a talking point.
Has let us down once. We had a card reader that had very little usage, that just decided to stop working. The security on these things is massive, and one tiny fault, and it will close down permanently the card reader. You can't reset the reader once this happens. We never did find out why, but our card reader committed suicide. iZettle wanted to charge us full price for a replacement, but we pleaded lack of use, and got it for free.