Speed is determined দ্বারা Internet not দ্বারা the site unless the লিঙ্ক are broken in which case speed wouldn't matter since they're broken anyways ;P
The sites I use most are watchanimeon.com - because it has the most shows and almost all of the ones I watch. Only bad thing is the লিঙ্ক are user provided and not really monitored so some might be broken and the quality differs from link to link.
For dubs I use watchcartoononline.com - Same as above ^