I think it depends on how regularly and long-term your band project is organized.
I always played in projects for at least 5 years and we had a PA and mixer for the whole band (sometimes even drums) in the rehearsal room, so I don't need my own monitors (well, sometimes before the season starts, we already play with In-Ears in the rehearsal room, to get used to it since we need it on stage... but that has nothing to do with amplification). So the levels are always mixed properly and I don't have to compete with guitar amps or the like... That is in my opinion the best way to go. Another advantage is, that you can hear how your patches sound in a real-world situation. Most bigger PAs don't sound as Hi-Fi as your studio-monitors or headphones (they are big and loud and you never now what the sound engineer is doing to you ;-) ). You can hear how your presets sound on a rather "shitty" system. If they sound good there as well, you can go on stage without any worries ;-)
For some special acts and rather spontaneous stuff, I have a big cheap full range active speaker, that suits all my needs, at least in an improvised rehearsal room. The speaker has pretty much power in the lower frequencies, so I think it would even do for bass playing. I don't know where you're living, but if you know Thomann and live somewhere to where they deliver, you can look, for their "the box PA 502 A" (don't know if links to online shops are allowed). The only problem is: it's rather heavy with about 30kg. I have this speaker for over 10 years now, and it still works withou any problems.
If you really need stereo in the rehearsal room, you could also buy two of the smaller and cheaper PA 302 A speakers.
But if your band plays together for several years, I would always prefer the first solution.