There isn't really much difference in respect of activities tbh.
The main difference is that the village centre is, just that at Whinfell with all the shops and swimming under a massive dome, with the pub, sports centre and spa a 5 min walk away round the lake.
The outdoor centre is quite a bit of a walk away from the centre but most things are all there.
At Sherwood the dome only encompasses the pool and the village centre is thus out in the open. Great in summer, not so good in poor weather (though on the flip side the dome at whinfell can feel a bit like being in a shopping mall).
Also at Sherwood the sports hall, outdoor centre and spa are near the car park (the spa being the furthest away) and quite a long way from the village. If you are at the other side of the park getting to these can be quite a hike (less of an issue if you have bikes). Similarly the pub is located away from centre and the other side from the sports/hall spa - but in a lovely location.
We like both for different reasons and tended to prefer Sherwood if going in summer/spring and Whinfell autumn/winter.
We tend not to take/hire bikes at Whinfell but always do at Sherwood as otherwise you have to factor quite a bit of time getting around the site to different activities.
The older accommodation is different styles (as they were originally different companies) but done inside to the same standard. The newer accommodations are pretty much the same though I think only Sherwood has treehouses (these are lovely and really enjoyable to stay in but super £££).
I think that's pretty much it.
We are pretty much in the middle of both so it's just a matter of preference for us. Tbh I'm not sure I'd favour one too much over the other if the travel time was a significant factor.