Hawthorns and Micklefireld send roughly equal numbers at 11+ to Reigate Grammar and to Dunnottar in Reigate. Dunnottar has given a very genuine option for those who can't or don't get a place at Reigate Grammar.
So Micklefield being Reigate based send the vast majority of their kids to Reigate Grammar or Dunnottar and then a small handful elsewhere. Hawthorns attracts families from a wider geographical area and also those indterested in boarding at senior level. Therefore they feed far more different senior schools and although send decent numbers to Reigtae Grammar and Dunnottar each year, are also sending to Caterham, Woldingham, Ardingly, Worth, Bedes, Whitgift, Trinity, Croydon High, Lingfield, Cranleigh, Hurst.
Choice of Prep depends on if you are dead set on one senior destination and pretty sure it can be achieved from that Prep. If you're not so dead set, the ones which feed a variety of senior schools might be better.
The senior schools will show their current coach routes on their websites....so people living in Oxted or Caterham or Crawley or Guildford or Epsom (north, south, east and west) can get to Reigate Grammar and Caterham will have similar north, south, east , west reach with the coaches too.
I do have to say, there is a big benefit to being able to walk to school whether it's at Prep level or more importantly at senior level when you just get lots of benefits of being close to lots of other local students and the flexibility to get home easily at any time which cannot be matched by even the best late coach routes.
With schools that are affiliated to specific senior schools, like Chinthurst or Reigate St Mary's you can feel the odd one out if not following the standard path....through choice or because you do t make the grade. It is something to consider.
But ask for exact figures from each school of their destinations for pupils moving on. Push for detail if they are vague.