I would much rather use Instapaper as long as the features are there. I don't really care about the social stuff. I care about the bookmarklet, and I care about the effort that Marco has put into making Instapaper the one major app I tell non-technical friends about (usually, responded with, "What, I click on the bookmark and it goes to my phone? Wow!").
I see no reason to change to Apple's version for Apple's sake.