So after trying out both banks for a couple of months, I decided Starling was the definite winner
Aside from the fact that Starling already have a current account and I find their app just a bit nicer to use, a key decider for me was their attitude to Android. Monzo are much further behind on Android and seem to treat their Android userbase as a bit of an afterthought. Yes, there are differences between iOS/Android with Starling too, but they seem to be making more of an effort to close the gap and have a stated aim of getting to parity and launching features in tandem going forward. To be fair to Monzo, their customer service bloke did say they plan to fix that (and indeed, their CEO has switched to an Android phone to lead by example) - but realistically it sounds like it will be well into next year, after they’ve launched their current accounts in full, by which point Starling will no doubt continue to have innovated.
Starling 1 - Monzo 0.