I for one can say I actually prefer Memmy. I think the themes look better and it functions a little smoother. I’m sure Mlem will be good though, it just seems earlier on in development.
Haha yeah we're definitely the "slow and steady" team on this one. Memmy is done in react-native, which, as the app very effectively demonstrates, is a fantastic framework for getting a smooth app out to market fast. We're using SwiftUI, which has the advantage of being the native iOS framework--it's more powerful and integrates better with the platform, but at the cost of being slower to develop in.
I tried both and they both have their strengths and weaknesses. Both are far from complete so it’ll be interesting to see how they develop.
That being said, long term my money is on Mlem over Memmy simply because Mlem is a native iOS app written in Swift and Memmy is made using React Native. In the end you can never beat the quality of a native app using a cross-platform toolkit.