I'll stick my neck on the line here & say I never fed anything but Wagg Guinea Pig Crunch because it's the only one recommended to me by the CCT.
If you look closely at the ingredients, it doesn't have sugar beet pulp or colourants unlike some others.
Science Selective has sugar beet pulp & salt added (why?) Added salt may cause piggies to drink more if they are eating these pellets.
It also lists as it's first ingredient Alfalfa, which is not supposed to be given to adult pigs in any great quantity so why would you want to feed it every day?!
Check the ingredients here:
http://www.seapets.co.uk/products/p...ience-selective-guinea-pig-complete-350g.html
Burgess also has salt, Lucerne (in other words alfalfa!) and sugar beet pulp in it rolleyes you have to look at what order these are listed, the first one is what the majority of the feed is made up from.
Guinea Lynx says you should avoid sugar beet pulp wherever possible:
http://www.guinealynx.info/pellets.html
On this basis, as Wagg Guinea Crunch has no added pulp or salt I would use it above anything else even though it is cheap. The CCT has done a lot of looking into all this & I trust their experience of over 30 years
I will also say it may be a coincidence but my first pair of piggies both developed bladder stones, then I switched to Wagg & my last two never suffered with them.