i owned a MWXT after a microwave 1. i sold the 1 when the XT came out because i thought the XT would be everything the 1 was and more.... but, i was wrong. after a few years i never gelled with the XT... despite all the knobs and filters, to me, there was a huge difference in sound quality between it and the analog filters of the microwave 1. a couple years ago i finally sold the XT and bought a 1 again and couldn't be happier. though i wish the microwave 1 had a high pass filter.. it's my only real complaint.
i haven't had the XT and the blofeld at the same time, so no direct comparisons.. but, from what i remember about the XT the blofeld is a lot cleaner and smoother sounding. it also has a ton of modulation.. with a similar matrix as the XT... looping envelope and stuff like that.
it has a bunch of filters, but not quite as bizarre as the XT's filters.
if i had to keep one.. my microwave 1 or the blofeld, it would be the microwave... just because it's one of my all-time favorite synths and there's something about the analog filters (vs the digital on the blofeld/xt) that have a nicer sound.
i don't think you'd need to rush out and get a blofeld if you had the XT... and the interface of the XT is more friendly than the blofeld.
i hear, despite having the same wavetables as the microwaves, that the blofeld sounds more like the waldorf Q... i've never played a Q so i can't confirm this myself...