Totally depends where and what type of riding you plan on doing. I have a MTB for riding river trails around where I live (my fun bike) but also a road bike cos I used to do tris. Now ride some TT's and road events. Usually have one or two road rides a week (Sunday group ride and midweek hills ride)

We are about to move to Ireland and rather unsure of what to take/buy. Think I will leave my roadie here for trips back (plan on about 3 of a months duration each year) and decide when we get there. Have been in touch with some cycling clubs, but they seem pretty heavy on racing. A hybrid would be handy for commuting, but Dublin traffic is mental and the MTB scene there is pretty small but hardcore and a lot of the trails in the Wicklows south of Dublin have been closed due to walkers protesting. Sorry to digress!