I think academically both schools are on a par. Kelvindale has changed over recent years by virtue of the fact that a lot of schools closed in 2009 in the neighbouring area of Maryhill. Kelvindale took up many of these pupils and some people felt it's been a bit straining at the seams since then. Renovation work is starting in Summer 2015 and it's well-needed as the fabric of the building is in fairly poor condition (as are the toilets). There may be some disruption during school year 2015-16 but the pupils aren't getting decanted so will work round it.
Knightswood has a newer school building and seems to have a friendly ethos. Lots of positive things going on with playground mentoring and anti-bullying strategies. Don't know anyone with kids there so can't tell whether this is just website PR or if it translates into real life!
What I would strongly advise is that you try and visit both schools just before the lunch hour. Get a tour during lesson times and then ask to see the playground hopefully when the kids are out there. Always a good indicator in my opinion. Watch for the level of supervision the kids get, the type of games they are playing and the language you are hearing 
.
On first impressions, Kelvindale Primary seems to have better outside space with a huge astro-turfed pitch and lovely woodland areas. However, the kids don't actually get to play in the wooded areas during playtimes and are only allowed there for occasional visits during themed lessons. Health and safety and/or lack of staff to give adequate supervision, prevents them going there at other times. The pitch is great but at playtimes can become a bit of a free-for-all and from what I've heard there's a lot of physical fighting "play" going on that gets either missed, ignored or tolerated. It also means that a lot of the play on there is football orientated.
Hopefully you'll get some more info. on Knightswood and I would be interested in hearing this. Have you thought about any other schools ie. Hyndland? I was going to say Hillhead but that place seems to be at crisis point in terms of numbers judging by the thread on here! Broomhill has good reports but I think they're getting their school rebuilt very shortly or even now.
I'm just off to start a thread asking about Hyndland Primary now!
HTH