For a factory, out-of-the-box action, the Tikka truly has the smoothest action - actually, it is much smoother than the Sako (not necessarily better than the Sako, but smoother - no doubt.)
However, if you take, say, a winchester or remington bolt action, and have it lapped, then it will be as smooth as glass. I had my Winchester M70 Classic Stainless in .375H&H's action lapped and I just can't believe it!! :eek: When you work the action, it requires less effort, and when you pull the bolt, it is super quiet. As such, the smoothest action I own is the that worked-on Winchester, but that's because I spent (if I remember correctly) something like $100 for the gunsmith's charges - maybe more.
Zachary