I think it would be best to keep your options open . Why not be both club & mobile dj? The mixing skills you learn from doing clubs can be invaluable for mobile work. Mobile DJ work is not all about weddings. Their are a host of possibilities like 21sts, Company functions, Kids parties , etc etc. The scope of work & the music is extremely broad. The definitive tastes of the guests can be extremely broad too! For example week to week one night may be all top 40 music the next is a mix of old school & new music.
Club deejaying can also be vast & varied too a lesser degree , many clubs play one style but others may have nights where its a different flavour.
A key point is to ask yourself musically where does your passion lie. If your preference is broad & open & you love lots of different music styles then go with mobile deejay work.If its limited to a particular style be it hip hop , r&b, dub step or whatever then club work would be your best option.
I have had deejays that have been solely into house music & made the mistake a couple of times sending them out to a wedding function . Even though i supplied the cross section of music required for the event , there passion wasn't there & they didn't enjoy what they were doing in playing old school party music.
So again where your musical passions lie should determine your deejay direction.