I'm not sure what the best food is, a food specifically for guinea pigs is essential as they cannot produce their own vitamin C so guinea pig food usually has it added. Rabbit food can contain anti-biotics and things which aren't suitable for piggies.
A lot of people find that a nugget food is the best value for them as some guineas will selectively eat from a muesli type food meaning they end up throwing quite a lot away.
I'm currently feeding my two Supreme Science Selective which is a complete nugget. I paid about £11 for 5 kgs, and they never leave any of it. However I'm currently mixing in a little of Oxbow Cavy Cuisine into their food as it has a lower calcium rate, this is a bit more expensive at £13.99 for 4.5 kgs (£9.89 for £2.25).
Because Coco is under six months old, they have their bowls topped up all the time but when is older I will reduce the amount of dry food they get to about an egg cup each per day.
I think Burgess Excel goes down quite well with a lot of piggies and is pretty much the same as the Pets at Home nuggets. Wagg Optimum is another good one I believe.
When I was interested in using Science Selective originally I sent Supreme an email, explaining I would like to try it but would like to check they liked it first and they sent me some samples
