Holmbury is typically the driest hill. Leith/Winterfold always boggy in the wet and Pitch somewhere in the middle.
Walking Bottom car park is always busy (i.e. full), you will be better off parking elsewhere and riding there. There is a map of Hurtmore car parks – google it. The one half way up Radnor Road out of Peaslake is generally quiet, from there you can either ride to the top of Holmbury, up from car park turn left off Radnor road at metal gate by underground reservoir to meet other riders and ask, or turn right at same gate to pick up trail Barry Knows Best (which is so well known I can’t possibly get flamed for mentioning it) and then ride to Walking Bottom.
If you like what you see you can join guided rides or shop rides (from Nirvana for example)
EDIT: If you want to ride from Wotton Hatch, then get yourself to the top of Leith via Bridleway and Woolverns Lane (some single track next to barbed wire fence but be careful of people using it as a descent, the lane is sandy so rubbish to ride/up down). From top you can meet some riders and look for Summer Lightening (official m arked trail) which you can follow most of the way down and/or some other trails which run down towards the Pub in Coldharbour. There are a few bomb hole areas to play around in – just ask. Afterwards for a bit of XC you can cross the A25 and follow Surrey Cycle Way (number 22 ?) through Abinger Roughs to and then cut back to the car.
Take a map, it’s easy to get lost.
If you fancy it you can roll into Deliverance – a big steepish section with some roots and a tree to crash into 🙂