Purcell --- Based on contemporary references to his humor and forgiving attitude toward musicians, one would like to think he might have been a friendly sort.
Handel --- Apparently had a very high opinion of himself and nearly got himself killed because of it (duel with Mattheson). He could be quick-tempered. I get the impression Handel could be stand-offish. While having guests, he would serve them the cheap port while excusing himself to sip the good stuff from his own liquor cabinet. I'm not sure Handel would have been all that much to hang out with. You could get to know him, enjoy his company, but perhaps not well.
Bach --- His son commented on his serious temperament, especially as concerns music. As far as music went, Bach did not suffer fools gladly or gracefully. If you were a musician, God help you. You'd better be a good one. Personality-wise, he seem to enjoy his beer, tobacco and wives (21 children). He also was said to have a healthy sense of humor. He was an extremely busy man and so probably didn't go to the pub very often, but if you had caught him at the Kneiper, he probably would have made a solid impression, a serious but buoyant personality who would have made you laugh with some biting comments concerning politics, the church and other musicians. Beyond that, he seems to have kept to his music, his family, and his home fire.
Haydn --- Haydn was said to have had in impish sense of humor and was well-liked, it seems, by nearly everyone who met him. A lady of high society was once in the presence of Haydn and Mozart while they conversed and said they were both bores -- talking of nothing of interest beyond music. Oh, to have been a fly on that wall.... I think you would have found Haydn unfailingly polite, pleasant and of good humor.
Mozart --- Mozart seems to have been well-known about town and quickly recognized. He must have been readily recognizable in personality and presence. One gets the sense from his many letters that he could be impish, playful, tender, kind and very vain --- very, very vain, but not arrogant. Perhaps endearingly so. He was likely much more approachable than Bach or Handel. He seemed perfectly happy hanging out with the hoy-poloi [sic] of the musical establishment --- something Bach never would have done and Haydn less likely.
Beethoven --- Beethoven was said to be charming, gregarious and approachable when young, but current theory has it that he suffered severe lead poisoning in his twenties (I think). This is thought to have had a profound affect on his personality and health. Beethoven, as most know, could be very short tempered, did not suffer fools, and was unforgiving of those stupid enough to question his musical judgement in any way. He must have liked the company of others,despite his reputation, as he frequented pubs and restaurants. His earpiece still survives, so he must have enjoyed conversation as far as possible. He could also be tender, loyal and liked to laugh (so we're told by contemporaries). I think, in his older years, Beethoven would have been difficult to know on a personal level. He seems to have enjoyed politics and the subject engaged him.
More speculation?