As an English tutor, my advice for students is to find a teacher you feel comfortable speaking with and with whom you enjoy speaking with. Of course, lessons should be productive as well!

I have stuck with one this time around, but I was thinking of taking some "instant tutoring" with others just for some conversation practice. I will stick with my one teacher for lessons, i think.

Try several teachers. I always do. You can choose the one you get on with best. And I really do think it's important to vary your language input - different teaching methods and accents. Stick with one main teacher maybe, but shop around too!

I don't know, as I haven't tried, sorry. But - if you stick to one teacher, how can you know if that teacher is any good or not? If you try a couple of different ones, you can see which ones you get on well with, and which ones actually know the language, and can teach well. From having seen some of the answers offered by particularly non-native speakers on here, it's clear that several of them do not have a very advanced level of English.