I used to recommend Vanguard, but not anymore since they sold their small business retirement plans to Ascensus.
Between eTrade, Schwab, and Fidelity, only eTrade and Schwab offer Roth options. eTrade is the only one that lets you borrow from your 401k, and it’s the most flexible with rollovers.
When it comes to contributions, eTrade and Fidelity allow you to contribute electronically, but Schwab requires you to either mail or deposit a check at their branch. Alternatively, you can transfer funds to a Schwab brokerage account, then upload your contribution form, include a signed letter, and either call support or use their online chat. I found the online chat to be easy, and they processed my contribution about a week after I made the request.