So, having now ridden The Smiler twice, both at the front and the back, these are my thoughts.
First of all, the debate over whether Smiler is better than Nemesis isn't even close in my opinion. Smiler is a good coaster, a very good coaster, but it simply doesn't compare to the might of Nemesis. Mostly, this comes down to how they've both been manufactured, and while I admire Gertslauer's will to improve and build bigger and better coasters, it's clear from how poorly the trains transition through those last 3 inversions, that they're still a long way off challenging the likes of B&M and Intamin.
I think the thing for me is that we're comparing a brand new shiny coaster with a ride that is now 18 years old, and that has to be taken into consideration. Given how The Smiler currently rides, and baring in mind Gertslauer's other coasters, such as Saw and Rage, I'd worry it'll ride badly in 3 or 4 years time, let alone 18.
The Smiler does a lot of things really well. Nemesis does just about everything brilliantly - and that's the difference.
That's not to say that The Smiler isn't a fantastic and much needed additional to Alton Towers' ride line-up, because it is. It has an intriguing theme that works. The Marmaliser is a totally unique piece of theming, and it looks great off-ride - especially when the 2 trains duel, but for me, Nemesis continues to be the jewel in the crown at Alton Towers.