savage,better action but between the 2 listed,howa by far

Its alot easier, you also dont have to true the bolt, it has one of the easiest adjusting triggers, not to mention the best trigger out. They have probably the best factory made barrel available on a out of the box gun. Gun smiths dont like to mess with the newer Savages because there is not much that they can do to improve them. The only thing I can say that I dont like about the new Savages is it has a weak extractor.

Howa.

It already has about the strongest extractor you can get on a push feed bolt.
The receiver is a flat bottom design which lends itself to better bedding than a round receiver.
The recoil lug is a tapered design integral to the receiver.
After market triggers are available from Timney, Jard, and Rifle Basix.

The only down side to doing a Howa VS. a Remington is that the Howa has metric threads and some gunsmiths lathes are not set up to do metric threads.

Gunsmiths like to use the Remington because they are absolutely every where, they're cheap to acquire, and a round receiver is easier to work on than a flat bottom receiver. They're kind of like the Chevy camaro or Ford mustang of rifle actions. But that doesn't mean they are necessarily the best action to build on.

Neither. By the time you spent the money truing a 700 or Howa action, you will have spent as much, or less, on a true custom action. The Savage target action is a great option.

The Stiller Predator action is also a GREAT hunting rifle platform on a budget. I have had 3 stillers, 2 panda-style Vipers and a Predator, and all 3 have been fantastic. The nice part of a Predator is that it's a drop-in 700 replacement, so fitting triggers, stocks, and bedding blocks can be done by the shooter.

Moving forward, my long range hunting rigs will be built on Savage target actions, since I've had so much luck with my Savage factory rifles, and I LOVE the idea of swapping out my own barrels and bolt heads.

Remmy. $550-ish for sps and my gunsmith charges $150 to accurize.

Savage would be another route, not sure if it needs blueprinted, but sss offers true and time for $125

If money isn't a issue then go the custom action route but $1K, no trigger, no floorplate. But no trueing needed.

Of the 2 choices, the Remmy 700 for sure.

BUT......as was previously posted, you can get quite a bit of money tied up in getting the 700 "tweaked" to where it needs to be.

I was just in the same boat as you...trying to decide on an action to start a custom build.

After I looked at everything, I wound up buying a Stiller Predator action.
Super tight tolerences, already "tweaked", got a Jewell trigger to go with it, and was able to DRIVE to Jerry's shop and pick it up instead of doing it all through the mail.
If you're intersted, contact Jerry at SPF (Stiller's Precision Firearms) in Wylie, TX. He was a super good guy to deal with.

The 700 would be my choice of those you listed but probably a CZ 550 American action would be my first choice.

m700 or custom clone, such as a bat repeater, 10x makes a nice one for $825. http://10xshootingsupplies.com/accessories_actions.html