Hi, i have a JX305 and i am as satisfied about it as i would have bought an MC505. The price is about the same here and i prefer keys anyway. The JX305 has also a mixer but it is a software one. The sliders are viewable in it's display when you call the mixer up. Shopprices here are 1250 US $ for both. It's a great thing with some nice sounds and lots of cool patterns.
When you go hear it in a store, it sells almost itself because the patterns are impressive. I haven't heared the EG-101 yet but i suppose it is in the same line as 303,505 and 305. The EG-101 should be cheaper (around 890US$) and easier to play (1-fingerchords and stuff). Soon we only have to push one button for a complete song, lol.
OH, i forgot one thing to notice. The JX305 has nice effects on board. I like the slicer effect most of all !! Combined with strings it gives a great and useable! sound. Have fun !