Allow me to begin by saying that I'm assembling the Liberty nickel series in grades of AU, maybe lower mint state. (My personal criteria tend to be stricter than the graders based on comparison) Down to the final four (1885, 1886, 1894 and 1912s) I'm looking at graded specimes only, and for the obvious reasons, with the intent of freeing them from a plastic tomb. The question is, would you buy one of the top two graders to do so? Part of me feels that it would be wrong as the chances increase of it coming back with a like grade should I ever chose to have it regraded. Which is something I've heard but not done. The only one I have cracked out thus far is an 1890 ICG MS63 which in my honest opinion would be an AU55/58. Which is more or less what I expected from a minor grading firm. Am I better off staying with the less used graders for this purpose?
Here, here. Buy the coin, not the holder. Good stuff to be had in any holder indeed, be it top tier or basement bottom. The final judgement rests on you, the collector.
My personal experience with doing the same is ICG and ANACS were right in line with how I graded, and prices were overall less than the top two. I did not do MS but AU or in some cases XF45.
If you are looking for the best deal, it is more likely that you will find value in an ICG or Anacs slab. With PCGS or NGC you will be paying a premium in most cases and you are correct that it could always come back a lower grade if you decide to send it back in. In the end, I would go with what some of the others said, find the nicest coin that you can regardless of slab but I will also add that the dollar value of the coin matters too. The more expensive it is, the more risk there is in cracking. Now if the amount fits into your budget and you enjoy the coin (and completeness of your set), then don't worry too much about a potential grade downgrade in the future.