Dublin Airport is an absolute breeze to get through if you have Fast-Track Security. Seriously, in T1 especially I am routinely through the checkpoint in two to four minutes. A ten minute wait would be outrageous and unusual, it's THAT efficient. It's also easy to walk to gates from Security so you really can actively cut it very fine on arrival to avoid having to loiter in the terminals. I wouldn't say that for anywhere else, mind you, but I fly out of DUB 10-20 times each year and it's always great.

I would probably suggest sticking with BA over LHR for your first six months and then switching if you decide to stay permanently. In my own personal life, I arrived in Dublin as a Qantas Frequent Flyer in 2005 and switched to BA in 2011 once I knew I'd be here a long time. I'm still with BA as a Gold member and stay with that, because of the advantages I get from a lounge access perspective in the oneworld alliance, especially as I travel to Australia every year to see family. The only reason I have not switched to EI is solely because they left oneworld. Otherwise I'd use them all the time.

Otherwise if you do switch to EI, you are going to have lounge access and Fast-Track etc, but again, you get all this with a BA card in Dublin. Some of your destinations EI don't serve, so you will have to connect over LHR anyway, so it's a tricky one!

The only other tip is to book AerSpace on routes that have it, as you get plenty of Tier Credits and you'll get EI status faster.