300 matches in Brawl mode
yay for math:
Assuming you take about 20-30 seconds to press start, pick a stage, suicide, do victory screen(with one stock against a com) then go back and repeat the cycle. it will take:
about 1 hour 20 minutes to 2 hours to unlock Sonic using Brawl matches. Whereas the SSE takes about 6-10 hours(according to Nintendo). So suiciding with one stock is the way to go if you just want sonic ASAP.
But if you want to unlock all the characters with 1 stock suicide brawls it will take:
2 hours 10 minutes-3 hours
Still faster than SSE(it's 450 Brawls to unlock Wolf)
However that will be mindnumbingly menotinous.