You might want to consult police.uk Sutton is very safe (lower crime rate than Guildford and the national average). Guildford is v safe too, though.
Sutton is actually in London with lots of train lines, direct to Victoria, London Bridge (short walk over the river to the City of London if you work in finance) as well as London St Pancras via City Thameslink. It’s also a short bus ride from the tube (runs 24/7) and you can use London taxis/Uber etc. Victoria and LB trains take 30 mins.
Schools are better in Sutton too as you get v high achieving primaries, excellent non-selective secondaries + you can apply for selective grammar schools as an in-catchment applicant (they’re some of the top performing state schools in the country).
Generally, Sutton and surrounds are great for families with lots of things to do.
What’s nicer about Guildford is that is has a nicer town centre (prettier + better shops) and it’s very close to the South Downs National Park.
The town centre in Sutton isn’t charming but v useful (essential shops, some nice restaurants and cafes, a lovely cinema etc). Parts are very leafy and it does back onto the countryside + you’re never further than 5-10mins from a park (80 or 90 parks in the borough). Having said that, Carshalton Village is very pretty and Cheam Village, South Sutton (incl Belmont Village) and Carshalton Beeches are all leafy, lovely and sought after.
Areas such as West Sutton, North Cheam or Sutton Common are cheaper. They do have fantastic school catchments and are convenient for shops, parks and leisure centres (incl the vast Sutton Sports Village). However, they’re less green and some parts don’t feel v lovely.