I loved NextIssue, but it stopped working on my tablet (Android) and it was a known issue they didn't feel like resolving.
I use Zinio and Google Play Magazines now, depending on which magazine I'm subscribing to. More and more of them are on Google now so I hope to eventually have them all there.

But Zinio gets crazy sometimes and offers you free subscriptions to magazines randomly, so I just can't quit them! They lure me back in!
A lot of magazines give print subscribers free access to the digital versions, so the doctors I work for let me have the free digital versions of all the mags in our waiting room because I'm the only one with a tablet. Score!