That's like asking if Ford or Chevy is better :roll: Both have their strong and weak points. Are you asking about current-production rifles, or, say the pre-'64 model 70s? What price range? Are we talking about just the actions or the whole gun?
The pre-64's are good, but still not the best. The Remington model 700 is every bit as good as post-'64 model 70s (when Winchester changed to a push feed action, which the 700 also uses). Both models have strong actions, mauser-style ejectors, and are good-looking guns. Most production years of the 700 had better-quality and more accurate barrels than the 70, but anymore they're all about equal. The edge goes to the 700 though. It's kinda like the Chevy of the group, where the 70 is the Ford - more parts are available to hot rod the 700 easily, but someone so inclined can still build a Ford to beat a Chevy. I also prefer the looks of the 700 over the 70.
So there's one choice.
My top choice over a 70 would be a Dakota model 76 classic. Imagine everything you could do to soup up a pre-'64 model 70, stick a model 700 magazine box on it and you've got the model 76. One built to my specs would run about $6,000
My next choice would be a T/C Encore, given certain upgrades. With a break-action single shot rifle, you don't have feeding problems. You don't have a bolt that needs to be 'squared up' for accuracy. The action is far simpler, with fewer things to break or go wrong, and its easier to operate. It's also more versatile, as you can swap calibers quickly and easily.
In case you veto any of my choices, I'll throw in a couple others. The Blazer model 93. Fully-supported action, straight pull bolt and 100% reliable. Also obscenely expensive. I also like the Barrett M468. It's built on an AR-10-style chassis, but machined to higher tolerances. Feeding is 100% reliable, it's fully anodized, the barrel is chrome-lined, will last forever and will never rust, but it only comes in 6.8 SPC. Doesn't matter to me though - that's a perfect round for hunting, self defense and combat for those so inclined.