I'd definitely recommend finding a shared ownership group if you can. The PFA used to produce a booklet on the ins and outs of group flying and it's probably still available from the LAA.
I'd say look for a group that has a proper constitution, is friendly, open and genuinely democratic and not controlled or dominated by one person. These often seem to be the aircraft's original or even actual owner which is why I personally wouldn't go for a non-equity group or the group's founder so make sure that you're required to meet several members before they'll take you.
Our group is a dozen and that seems about right to us for a sensible balance between costs and availability.The cost saving is the obvious advantage. If the fixed and flying costs are properly allocated you need to fly at least 10-12 hours a year to realise a good saving but the far cheaper hourly cost compared with renting means that the more you fly the cheaper each hour becomes.
The other advantages are less obvious. With a decent booking system you can fly the plane more or less when you like and far less formally than hiring; and if you want to go somewhere overnight you don't have to ask permission; you've always got a group of people you know you can call on if you want to share flying and there is also the sense of ownership, that it's YOUR aircraft.
When I went from ad hoc hiring to group flying my annual hours more or less doubled and the types of flying I was doing also got a lot more varied. I've been flying in a group for about fifteen years and I'd never want to go back to renting.