Hello akhil , its very good to see that you have a goal and you are focused towards it. B.Arch is a bachelors in architecture course of five years offered by various collegs in various states of India and abroad. The choice of city is not a factor you should be looking for an admission in ypur desired course, you should choose from the list of good colleges that are present. This can be done by keeping in mind various factors like opportunities, internships, projects, fees, placements , etc offered by the college. 

Further if yo still want to choose from a list of cities pune is much better than mumbai for B.Arch courses as the number of good colleges with excellent oppotunities are present there. Rest the choice is yours, choose wisely.