hi Arthur_dent...
Can't say i've ever lived in Bristol, but have been making truck deliveries in and around the area for the last 10 years. I have grown up about 20 miles north of the Bristol.
hollyberrys description of Bristol and Bath is spot on. Both have two universities, and specialist industries. In my opinion Bath trades on it's world heritage status and roman baths to much and as such never feels as though it is lived in...
The public transport links between the two cities are OK...they are expensive, but a regular bus service runs every 15 minutes or so.
However Bristol has some of the worst congestion in the country...worse than London in my opinion!!
(not helped by road closures and improvement works going on at the moment!)
So if you are planning to commute i would factor that into where you buy!
on the plus side Bristol has ALOT for kids to see and do...the museum, the aqaurium, @bristol and the zoo. Plus the annual Harbour and food festivals, and Aardman animation are also here so they usually get involved in the fun a few times a year! There are also lots of parks, the Downs and Ashton Court are both free council run parks which are well used by the communites...and lots of things are usually free, or just a chill and relax on the harbourside...and LOTS of shopping opportunities in Bristol.
As for Portishead? It is basically a commuter town. It has a few large chains like co-op, lidl and waitrose, but mostly it's a local high street with independant shops. until recently it was a relatively small town but they have just built a massive new housing development, with some new bars along the marina. (so again big increase in commuter numbers into bristol)
If you are used to the beaches, sadly you'd need to travel to Weston-super-Mare for that, but easy to get to by car of train.
If you are looking out of the city, i would suggest places like Thornbury/Wotton-under-Edge/Dursley area. (I might be biased as this is where i grew up!) but they have all retained their own character whilst only being 30-45 minutes out of Bristol...
but a car would be essential as public transport is an issue out in the coutryside
I am currently looking to buy my first place in Gloucester, and have found that rightmove will map the local schools and a provides a direct link to the ofsted report if that's of any help.
Best of luck with your move!