One of my favourite amps is the Marshall I've had since I started playing guitar.
The amp I prefer to use for the most part, however, is a peavey.
It's horses for courses. None of the Marshalls I have do high gain stuff aswell as my Peavey 6505. But I prefer one of my marshalls for the cleans and another for the dirties.
It's like saying that a jigsaw isn't as good as a spirit level. Different tools for different applications. You can't beat a marshall for certain applications, but some amps will kicks it's ass for others.