I guess like all things it's down to preference. Personally the GSF styling does nothing for me. The only advantage would be the 5th seat, but there are plenty of other 5 seaters I'd choose first (other marks included). I think the RCF is nice but doesn't suit my lifestyle and again, the big grill front end is a bit 50 50 for me.
The ISF in its current form does it for me, style and shape wise. It might not be the best out of the block with its performance, but no car stays standard for me, so that's never been an issue. It also fits around my lifestyle and works better in the garage than it's bigger cousin the GS.
All-in-all, they're all fantastic cars and with the ultimate selling point, reliability!!