I'm a dance musician and I would like to hear honest opinions (/experiences) about which one of the above is the best synth to compose competetive, high-quality dance tracks with? Right now I'm on Rolands side (I'm thinking of buying the 305) but I'm still not 100% sure.
I would be grateful for some opinions!

hello...i've got jx-305 and i´m making dance and trance with it and it's extremely good for my purposes...quasimidi raven has better soundquality,more multimbrality,better effects and filters...sirius is quite same as jx305...the vocoder in sirius is very nice and you can make those kraftwerk-kind of robot voices and other really cool and impressive sounds...i think they all are good for dancemusic and it doesn't really matter which one you buy beacause you can make good dancemusic with all of them...

The Sirius is far superior to the JX305.
The quality of sounds and the drums just can`t be compared to the JX305.
I used to own a JX305 but sold it to buy a Sirius as when I heard it it was awesome.
It is also very easy to use.