Hey there for
You might want to check kvr -
http://www.kvraudio.com/forum/ - for more info. Just do a forum search there and you will find endless threads about subjective sound quality of synths, comparisons etc.
For what's it's worth though... I never liked the sound of ultra analog much personally - kind of analogue esque but very 'polite' if that's the right word. Sylenth is a different kettle of fish - fatter sounding oscillators and filters that have a decidedly modern sound as opposed to synths of the 70's and 80's. All subjective stuff... Best to just try the demos...