Navbox Pro for me, for VFR.
Flitestar IFR, for IFR/airways. Has specific features for IFR like semi-intelligent (I almost said "intelligent" but it crashes too much) airways handling - put in the airway sequence and it generates the route and a plog with all the waypoints.
Flitestar is not a nice piece of software. It crashes regularly, in fact every time with certain routes loaded, and for VFR it offers little that Navbox doesn't offer. I suppose Flitestar VFR is good if you buy the VFR raster charts; then you can print off enroute sections which is quite slick - for long range European touring. But for the UK, VFR, I would use Navbox every time.