We've stayed at both - Courtilles de Lido was a long time ago, and I can't remember a problem with site access. It has nice big grassy pitches, hedged between, the washblocks are fine - although the showers were on tokens when we were there, and the token didn't last long enough. I didn't have any more tokens, and therefore had to run across the washblock to rinse off the shampoo. (I think that may have changed since). There's a smallish pool, and the biggest drawback is the train noise as the train track seems to go around three sides of the site! It doesn't actually, but that's where the sound seems to come from. Moiret sur Loing, the little town nearby, is lovely, with some good restaurants, and you're handy for Paris and Fontainbleau.
We've stayed loads of times at Lac de Panthier - last time was in May last year but just for two days. We had a lakeside pitch (some of them are huge)and a lovely view out over the lake. The site is split into two halves - one nearest to reception and with the indoor pool, bar and restaurant, and the other a short walk down a lane, with the outdoor pools. Washblocks are fine on both parts of the site - not state of the art, but kept clean, and with powerful hot showers. There are quite a lot of 'tour operator' tents and mobiles there, and it does seem to be a bit of a transit stop as it's just off the main routes to the south so people seem to be coming and going a lot. In very wet weather the pitches can become waterlogged - and one year we had 'duckboards' from the path to the tent! The site restaurant is not fantastic (but the pizzas were!!) - and we've had one very disappointing dish there - but the views from the restaurant are lovely. The surroundings are typical rolling Burgundy hills, with white Charolais cows in the fields. Chateauneuf (nearby) is worth a visit, with a lovely castle, and there's the Chateau at Commarin. Nearest supermarket is about 5 kilometres away - though there's a small 'Shopi' nearer.