OK, I have to say I'm not too interested in e-piano and e-organ sounds. In these sound categories I can't tell whether the Motif XF or the Integra is actually better. But regarding other sounds, my rating is as follows:
Grand piano: Integra 8 points out of 10, Motif XF 7 (I didn't like the Motif XS grand at all, artificially bright and obviously not 88-note sampled; the newer S6 sample is nice, but still the Integra's SN-A grand has a slight edge to me)
Brass: Integra 10, Motif XF 8 (Integra has some very good SN-A solo brass sounds, the Motif solo brass lacks the physical modeling engine, however the newly added trumpets are very nice; but the Integra clearly wins regarding sections due to the SRX 10 expansion board, very realistic C-trumpet, trombone and french horn sections. The Motif french horns sound artificial, the small/medium brass section is nice).
String sections are far better in the Integra, except the Motif's 'Section strings', which are very realistic, too, but represent a rather small section. The Motif's large strings are not realistic enough, especially the 'ensemble strings', a really poor sample. Solo strings are nice in the Motif.
Guitars are great in the Motif, the Integra's guitars are also partly extremely good, but some are so-so.
It's only my opinion, but regarding symphonic sounds I think I know what I am talking about, having played the trombone in a symphonic university orchestra for some time.
Of course, the big advantage of Motif XF/MoXF is the flexibility to load libraries into the flash, which can really turn it into a new instrument.