I have worked in 2 of them. I don't live in Exeter but from your list, the only one I would entertain for my kids would be Kings.
I disagree with the Steiner system and know one of the "elders" or whatever they are called at the Exeter school. I wouldn't put them in charge of sweeping the road, let alone educating my child for life.
Isca has improved massively over the years, but I don't know enough about it to comment.
St Luke's has had a number of issues. A friend's daughter spent all but half a term of year 11 there without a qualified science teacher. The school insisted on teaching the year 7s with a scientists, but not the top set of year 11. My own DD who is a year older was tutoring her to get her the C she needed for college. The Maths teaching there was also abysmal. Behaviour was a problem (not just the kids - I was bullied by someone thankfully no longer there and when I complained to the Deputy Head, she ignored it. I resigned and told the Head why I was going - the perpetrator was soon up the road as I wasn't the first, just the most vocal).
St James is not bad and worth considering. It takes a lot of kids whose first language is not English, but they make great progress and when I have been in there, I like the caring and calm atmosphere.
There is also Clyst Vale which is between Exeter and Kings. I wasn't overly impressed when I visited it some 9 years ago, but lots can change.
It is really hard to be objective, but as both a parent and teacher, I try to evaluate schools from both sides. If you want any more info, please PM me.