Uriel - you're the nav man here

Have you given it much of a spin?
I already owned the old TomTom app so got the upgrade to TomTom Go Mobile for 50p.
Just used it on a holiday to Cornwall but often checked it against Route 66. I've also run both concurrently for some journeys.
The routing is very similar but not identical. If traffic is detected prior to route planning, Route 66 usually gives it a wider berth, with a preference for main routes. TT Go will often stick closer to the default route but go for detours on side roads.
It seems that once the route is in progress, TT Go is a little more willing to reroute around traffic even for very minor delays. I think TT Go is doing something like checking for alternative routes in the background more often.
So far Route 66 is looking like getting my vote. It has a couple of important features over TomTom. One is the ability to select any part of the route and force it to avoid with a road block. This proved useful for me today when the TT traffic service both apps share didn't pick up the road closures for Sheffield's half marathon. TomTom Go will calculate alternative routes but it's a bit random. There's no way to tell the app where you specifically want to avoid. The other issue only really affects long journeys. TT Go has a traffic horizon of about 40 minutes for jams and 100 miles or so for road closures. R66's horizons are further. It sends to ignore jams further than an hour away but there doesn't seen to be a closure horizon. I've seen it plan route avoiding closed roads over 200 miles away and you can browse anywhere on the map for traffic.
They are both excellent navigation apps though. I would say the best there is for traffic avoidance with Route 66 having a slight edge. TT Go becomes more attractive for the price of you want worldwide coverage, speed cameras etc.
The R66 two year thing is a licensing issue. They licence the maps from TomTom and therefore can only offer updates for as long as their contact allows. I believe this must be a 2 year rolling contract. There's been a R66 app on android since 2011 iirc (vastly improved in 2013) and so far the free map updates have kept coming for all users. R66 customers have also been given free updates to new versions of the app (the 2013 update was an entirely new app rather than an update to the existing).