"better" in what way? there's plenty of artists that make better songs & albums than Em. "better" in just outright spitting, multis etc there's prob not many since he came out but there's more to being an MC than JUST how many syllables you can rhyme together.
you could say MF DOOM because even tho yes he was Zev Love X before that, DOOM is and was a complete departure from the KMD style of rhyming and subject matter etc, it's basically a whole new MC.
Lupe is def there from a spitting level
Tech N9ne is better than Em IMO
Em really only has the advantage when you talk about all out spitting but when you look at WHAT he says sometimes it's just stupid nonsense and his flow is all but gone since Relapse. every other aspect of MCing Em isn't up there anymore IMO