Nexus 7. I've got one. It's a billion times better than anything below its price point, just spend the extra.
to be honest when i started looking into the playbook I could see issues, chief among which was the lack of expandable memory and with running an android phone, using an android tab just seems sensible.
nexus7 is £200 (although the lad at work who is pretty well up on these things seems to remember seeing them for sale at about £160 somewhere very recently.) for the sake of £40 / £50 I would rather take a big jump forward in performance & suitability to my needs plus the bonus of what it can do on top of a cheaper tab should i want it to so it looks like i'm waiting a month or two for a good deal on a nexus and for a few more pennies to find their way into my bank!
The 8GB one is £159 on google play.
True enough, you can get a playbook with more storage for less, but the Nexus has a very impressive spec. My only reservations would be storage space, if there's no card slot, or I suppose USB host, that's quite restrictive.
Well that and 7" screen, as personally I've got a 10" tablet already, but is the Playbook is a consideration then the Nexus is a strong alternative.