The main difference seems to be that BitWarden is server software that added mobile, whereas 1Password is mobile software that added a server. So the former is pretty strong on the backend (robust API, can run your own, client-agnostic) whereas the latter works better on the client side, without the "glitching" that sadly is common on BW.

I've been a BW user for years (relatively early adopter), and they are improving. At the moment I wouldn't consider anything else, for the simple reason that I could host it myself tomorrow if they went closed-source or shut down. For something like secret management, continuity planning is a must IMHO. I think they have been very good at doing things The Right Way since early days. Also 1Password always looked very Apple-focused and I'm trying to move away from that.