Maybe both. I use them both.
For checking the feeds I use 6tag, since it is smoother and I can also save photos to my gallery. Also because it has more features, and some of them that are lacking in the official app and some featuures that aren't even in iOS and Android apps.
For uploading photos, I use Instagram BETA since it is the official app, so it doesn't hurt my account in any way (getting flagged or tagged as using 3rd party apps)