We did three hours for Stansted a couple of months ago, wasn't too stressful.

Was to Oslo. Chose Ryanair over BA because it was Stansted not Heathrow/Gatwick (can't remember which), cheaper and Ryanair's carry-on baggage policy was straightforward and simple to understand, unlike BA's.

If you will be travelling on a UK passport with carry-on get as near to the front of the plane as possible to get to the passport queue ahead of everyone else as you'll need to be stamped in to the EU.

And out again! At Oslo that was just before the gate which caught out quite a few people having to queue again at that point as they'd loitering too long over their vittles.