Sorry no one replied to this in two months. I hope it's not to late.
I'm a Guilford resident with a child who has high functioning autism as well. She's been through Guilford Public Schools since Kindergarten and I have never had any trouble with the schools' support of her needs. I should note that she has never needed an IEP, but does have a 504 Plan.
Sometimes I need to contact teachers (especially support teachers) to remind them on an individual basis what accommodations are expected through her 504, but I've never felt that Guilford lacked support.
Also, it should be noted that this coming year (2013/2014) will be the first for a new head of Special Education at the administrative level. I'm not sure what changes will occur due to the new position.
Guilford has four elementary schools: AW Cox, Calvin Leete, Guilford Lakes, and Melissa Jones. They're all wonderful and I would recommend any of them. I'm not as familiar with the elementary schools in Madison, but I do know that there are three of them, and two of them are part of larger campuses - Ryerson is teamed with Brown Middle School, and Jeffrey is part of the Polson Middle and Hand High campus. Island Ave is all by itself. I'd probably suggest the former two over the latter, if you decided to move to Madison.
I also have a close friend who is a teacher in Madison and, from what I can tell, they have similar support systems in place in their district. I've never heard my friend complain that they lack support at all.
Sorry I don't have a better answer! Best of luck to you; I'm sure whichever town you choose, you'll find good schools for your child.