Does file size matter for Google videos

I upload 2 videos on Google or YouTube.

The videos are of same length but different sizes: Video A is 50MB and Video B is 100MB.

Now when a user is watching these 2 videos, would google stream video A quicker than video B (because video A is smaller)?

Or does the size of the video would not matter because google will convert them to Flash?

I am asking this question to know whether to upload good quality/big size video OR low quality/small size videos on google. If I upload big size video, users will have to wait longer to watch them.

thanks