You really have a lot of options, and they depend on your style and type of shooting. The great 50/1.4 has already been mentioned, and the 1.8 is an undervalued little gem, in either black or chrome. A favorite of many is the 50/1.5, a Sonnar derivative, that has a nice look, and is very compact. The 1.2 also has many adherents, myself included.
For wides, I love the 35/2, but the 1.8 and the 2.8 also have many fans. The 28/3.5 is a tiny lens, generally relatively low priced, and a good performer.
Canon made many excellent lenses in the RF period, as did other makers. Of course, you can also use the Leica Summar/Summitar/Summicron, if you have them, and expect results that are very predictable.
It's a very versatile camera. The only nuisance is the lack of an acc clip, but that's not an issue with the usual lenses, as the finder is versatile, as well.
It handles very well, and isn't really heavy, considering the quality.
Harry