Earlswood has a different feel to it. It’s south of Redhill rather than north. It is mostly Victorian housing stock, rather than having 2 estates. I think it feels more part of Redhill than Merstham does snd you’d walk into Redhill faster from much of it. You’d also get to Reigate very quickly from there.
In terms of schools, Earlswood has the Infant and Junior school which are well regarded. The kids who live in Earlswood go to The Warwick or Reigate School or to St Bedes. The latter is a Church school with a 3 year Church attendance criteria. With the other 2 it depends which you are closest to. Reigate School is probably more sought after.
Earlswood has a station - it’s one stop down the line towards Brighton from Redhill, whereas Merstham is one stop up the line from Redhill. So if you’re a LOndon commuter, Merstham is a bit shorter journey.
Earlswood also has a post office/corner shop, a couple of pubs, an Indian restaurant, another takeaway. People would certainly go into Redhill for most shopping, or perhaps to Reigate. Earlswood Lakes are nearby and nice for a walk, plus there’s Earlswood Common. People generally like Earlswood for decent sized and priced family homes. Quite a lot of people move from Reigate for bigger homes which are more affordable, but who want to still be close to Reigate. It’s also good for getting to Horley and Gatwick.
Personally, I like Merstham too. It really is a place of different parts - Watercolour is pretty self contained, plus old Merstham and the main estate can feel quite separate. There have been other threads about Merstham before. Lots of people on those are wary of the estate. Quite a lot of it has been regenerated, plus remember that it covers a large area overall and there are different parts. To be honest, most areas have sections which are/were social housing and that includes Reigate and Redhill.
Visiting is a good idea. You really do have to look and visit several times and at different times of day to get a feel. If you’re very new to the area, renting for a period can help you get a feel for the different areas - like everywhere, even within a couple of roads, places can be quite different. Good luck.