I'd certainly heed Julian's advice on the different camps in April but would take issue with Chobe being "just elephants". We visited last month and saw a fantastic selection of game in a pretty short visit. There are a few photos on our website
Chobe is somewhere around page 25 onwards, I think
As this is the scenery section (the wildlife will come later - it takes quite a while to get them all loaded) then most of the animal shots are distant, and yes, some of them are boring old elephants, but there are probably Red Lechwe, buffalo, impala, waterbuck, Nile Monitors and so on.
One difference that Chobe can offer that may not be available in KNP is the chance of an escorted boat trip.
I've only spent 12 days in KNP in total and have only once seen more than about 4 vehicles at any sighting. I may have been very lucky and we've spent quite a lot of time in the centre and north of the park which is quieter. Sometimes last month we went for 30 minutes or more without even seeing another vehicle. We watched a group of 4 lionesses harassing a huge herd of buffalo on our own (near Pretoriuskop) and a mated pair very close to the road with just one other vehicle. I'm sure congestion does happen but as the vehicles have to remain on the roads and tracks then there's not much chasing of animals going on.
Anyway, in case anyone is put off by some of the comments above, Chobe in October is definitely worth a visit, because much of the wildlife is concentrated in easily accessible areas near the river. I haven't been to Okavango (yet) but would imagine it to be even better.