Hi Mike,
With the GGW, the path certainly tends to be sandwiched in between lochs and coniferous forest, with the forest often being on slopes. You can still find places to camp, but these are a lot more scarce than on the SSW. I really wouldn't let that put you off though, as it's possible to sniff out appealing places to camp if you persist and use your imagination! Just don't allow yourself yourself to be put off by psychological barriers!

As you'll see from our Great Glen Way Journal
http://www.adventurejournal.com/Great_Glen_Way/ all of our camp spots are squeezed in at the side of the trail; even at Abriachan, which has a paid "campsite", we were sited on thick moss in a clearing in a wood!
Of the designated wild campsites on the SSW, we saw Fiddich Park, Craigellachie ( a public park, with good space and toilets but we couldn't help but be worried about dog waste, Blacksboat Station ( we passed straight through, but looked a lovely spot either on the station platform or opposite the station, Ballindalloch Station (we camped on the platform and missed the attractive little site round the back, and Tomintoul (locals warned us it had been abused and there was human waste there).
Of course, don't forget that while the Speyside Way has official wild campsites, the Land Reform Act means that, with a few reasonable exceptions, you are not restricted as to where you can camp on either of the routes.
I think the more important question is one of trail quality. We greatly enjoyed the GGW, but wouldn't recommend the SSW - it was pretty mundane and quite a disappointment - imagine continual treks through farmland, fenced in, with the actual Spey river barely ever even in sight! Our addition to it from Tulloch to Aviemore was well worth doing though.
All the best, Alan