Hi Ange. Of the 3 locations you mention, Farnham is by far the nicest IMO. Farnham is a nice old town, with a really friendly feel to it, a good range of shops, train links to London, lovely river running through the edge of town with good walks along it. There's a great park next to the river with a lovely play area for kids, and there's a larger park up near the castle (did I mention it has a castle too?). Nice farmer's market every month, lots of places to sit and drink coffee. Close to lots of lovely countryside around the are too, so you're never far from fields and woodland (in fact Alice Holt forest is just down the road, fab for familys).
Fleet is a fairly new town, the town centre is not particularly attractive or exciting, the range of shops is pretty poor and, to be honest, it's somewhere I drive through but never stop at. There are really good train links to London from the station here though, and it's very close to the M3, so good for transport links. There are nice places close to Fleet (Hartley Wintney springs to mind, very nice indeed!).
Church Crookham? Very close to Fleet, just houses and small local shops really. Not terribly exciting (my brother lives there so I know it fairly well!).
Depends what you want from a place to live really, but of the 3 Farnham is my definate favourite. You could also look towards Guildford which is lovely....not that I'm biased!
Church