I suppose ideally OP would get a response from someone with current parental experience of both schools. I can't offer this, but am a current RH parent with a modest knowledge of Ravenstone through friend' kids, attendance at clubs & events, and so on.
As already pointed out, Ravenstone is light years ahead for on-site space. Rutherford's site is barely adequate for the number of kids it has. Morning drop-offs are a mess, though I can't say that this really matters much. Use of the playground has to be carefully staggered/shared between year groups. A couple of the RH classrooms [I think at least one of the ones at the very top of the school used to be a caretaker's office or similar back in the Balham Youth Court days?] at aren't the greatest.
The head at Rutherford is top notch, an absolute force of nature, but has been there a while & IMO seems unlikely to still be in post certainly by the time OP's son is moving through KS2. A number of things may change when she's gone, though of course the limited space won't be one of them.
I'm don't particularly think Rutherford would deserve a reputation for being "academic". It has a lot less compulsary homework than many ordinary primary schools [e.g. I can confirm this compared to Telferscot but don't have direct experience of Ravenstone]. I think really the 'academic' label is at least partly a euphemism for having expensive uniforms and relatively affluent parents who will quietly start paying for tutors once secondary school applications start to loom on the horizon.
Although RH has its share of 'state till eight' kids who slip into the private sector towards the mid-late stages of their journey through primary school, they seem, increasingly, slightly more successful than a lot of local places at filling the gaps that appear as a result. Maybe they need to be because of a funding imperative.
As already mentioned, after school provision is first rate. There's a huge choice of clubs & activities.
As already mentioned, the The PTA is good - there are a few grumbles about inclusivity which aren't totally without foundation but it's IMO probably less bad on this score than most PTA's.