rotom-f: holy damn, this is fantastic. until this point i had never really been a strong fan of rotom-s (heh pun) because i don't really like sr-weak scarfers whatsoever, but rotom-f far and away exceeded my expectations simply on offensive coverage alone. boltbeam stabs are absolutely amazing (plus you have a reliable one in hp ice) and if you don't need rotom-s's fighting resistance, i definitely encourage you to give this a try.
I prefer HP Ground - it goes really well with Blizzard (which is still a good move, even with 70% accuracy) and Volt Switch/Thunderbolt/Thunder, and allows Rotom-F to handle most Steel-types adequately. As a TrickScarfer I view Rotom-F to be the best in both NU and RU. Electric/Ice may not be terrific defensively, but it does allow you a lot of offensive merit both STAB-wise and coveragewise (you could even run HP Fire, or HP Fighting, and not lose any coverage potential).