I use Coconut, which i’ve been very pleased with to date. Very intuitive.
The only issue I currently have, which will be common for a number of the online only banks, is that they don’t have a facility to accept incoming cheques. I didn’t think I would need that functionality, until I received a VAT refund by cheque. I can set things up to receive future refunds via bank transfer, but still to work out how to deal with the cheque I currently have.