I heard about the too much bass they have.Is this true?
Nope. The bass is accurate, defined and well-extended on the M50's. If it's hyped at all along the frequency range I'd say there's a slight bump, and I mean
slight, as you get to the upper region but they don't seem nearly as bright or harsh as the Sony 7506 in that same area. Speaking of which, I haven't heard them myself but it's my understanding that the MDR 7510 is an update on the venerable 7506 and is a slightly more neutral headphone. The drawback being that the 7510 is plastic whereas the 7506 uses some metal in the construction.
Conversely, while the AKG's are wonderful casual listening headphones they seem, in general, to roll off the low-end and have a little sparkle in the high-end. Not truly flat. I found this with both the 240's and 270's I owned and in my limited experience with the 271's.
I have heard positive things about the Ultrasone headphones but don't have any personal experience with them.