I love Belleville. we don't actually visit Paris any more, just this studio and the cafe at the end of the street. every day we meet another local who tells us that this is their favourite suburb, that the day they found Belleville they moved there and will never leave.
Since last year the local wifi has really improved, and O'Paris (the cafe at the top of the park) has become so popular that you have to get there very early to get a seat. I recommend having breakfast there and staying for lunch and dinner.