I think the 4K edition is the way to go, because is has a blu-ray disc as well. All three versions of the film are present and they look amazing, and there are some extras that are new to that edition. And if you ever get a 4K capable device (such dedicated 4k/blu-ray player or current Xbox) you'll already have the 4k disk waiting.

Here's a link to that version on Amazon.

But if you still don't want to buy that version because of the 4K disc then I'd recommend this version of the blu-ray. It's got all the versions and extras as well. Funny enough it costs a little more than the 4K version on Amazon, but it's still affordable enough to be well worth it.

Edit: And to clarify, the 4K's blu-ray disc has the theatrical edition, special edition (with added scenes), and a third version that's the special edition with the alternate ending (and an extra scene with the T-1000 as I recall).

The same disc also has the bonus features, including a new 55 minute documentary. So even if you never use the 4k disc that edition is still absolutely worth it. (And it's cheaper than the regular blu-ray anyway).