Essex in general is better - Chelmsford has far better services, better support, better SEN schools, better SALT & OT help.
But North Essex? People move AWAY from here to get support, and the schools and North Essex LA are notorious for setting illegal blanket policies that have been challenged repeatedly in court, yet continue.
Over 15 years of dealing with DC's with ASD issues (and even being unable to get full dx on the NHS for 2/3 or 3/4 of them ), I would avoid avoid avoid. Only the very most severely Autistic DC's tend to actually recurve a FORMAL dx. And usually only then if they are disruptive in school, and have ADHD as a co morbid. It's probably the only reason DS3 at 25mo is so much further along the diagnostic procedures than DD at 15yo, DS2 at 9yo, and DS1 at 10yo - because he had been dxd as 'hyperactive with a high probability of ADHD' by the Paed by the time he was just 21mo! As the others don't have ADHD as a co morbid, all I got told was that they "have Autistic traits, they are somewhere on the spectrum" for the others, handed a bunch of leaflets, and left to get on with it...
If I wasn't tied here by PSO's from Ex partners, and living in Social Housing, I would be in Surrey like a shot!
The NHS services here are particularly bad too - no SALT therapies other than worksheets for non-verbal DC's, no dx given on specific SALT problem, no Centile assessments to ensure knowledge of level of difficulties. Specialist ASD SALT non-existant. No SALT in school apart from in the two SEN schools.
OT - waiting list of approximately 2 years to SEE OT, exercises given on worksheets then discharged to the care of the school (MS) who don't bother to implement the exercises at all. Getting equipment is nigh on impossible - most people here don't get Mac Majors or swifty's unless they have a dx of CP. Anything else is ignored. We ended up paying. Getting adaptations for the home or school is nigh on impossible too. Sensory OT non-existent.
Proprioception stuff IS OK through SEEPOK, but only if you can actually GET an appointment. DS2 is now 9.3yo and has been waiting since he was 11mo...
Any other sort of sensory integration therapy requires a long commute that is nigh on impossible if, like me, you are reliant on public transport.
Seriously - North Essex is one to steer clear of IMO!