Ryanair will make any effort they can to put you in the base you request, however sometimes that base is sometimes full. It might be the day of the week what bases are available due to movement within bases, upgrades, cadet training, pilots leaving or just plain requirement, but they will try their best.
Despite all the negative comments you will read here on Pprune there will be more positive you will hear once you get into linetraining or based somewhere and geet to know pilots in the system. Only few percentage are not happy but the ones that are happy just donīt bother making comments because they will probably be shot down on this forum for it. I am with Ryanair for a few years and I still like it. Hard work but paid well for it.