FWIW, I've been a frequent traveller to NI for around 12 years. I don't have any strong preferences for airports (even flew into CODA once!) or airlines (going back to BA, BMI Baby etc), it's almost always a combination of price vs schedule that wins the day for me.
I like EZY because it's often (but not always) cheaper and it's always a jet.
I like FlyBe because of the high frequency and sometimes it's a jet, I think if they reduced frequency on MAN-BHD, they would be quite unlikely to see any of my business again. Frequency is the key difference between the two options which is why sometimes I do pay more to go with FlyBe.