Welcome to Flyertalk, sambalgado!
Do you expect to mostly fly economy/expensive economy or business/first?
If you frequently travel to the UK, look into the bmi programme. Otherwise, I'd choose a Skyteam one (OK+ or Flying Blue) and connect in PRG or AMS or even CDG instead of chancing it with London. 8 trips by four segments (for example one trip DUB-PRG-XYZ-PRG-DUB counts as four segments) will net you Gold in either programme, which means lounge access.