I use the Rodipet young Syrian mix and mix it 50/50 with Bunny Dream Syrian hamster food from Zooplus. The rodipet food is a bit expensive. To be honest if you want a mix that provides everything, hamsters enjoy and gives variety, then you can't really go wrong with Harry Hamster which is probably available on Amazon (and tends to be in most countries). It doesn't have the quality of ingredients of the Rodipet and Bunny foods, but they are low in protein so the protein needs supplementing. Harry Hamster has the correct protein levels. I quite like it - it has whole peanuts in shells in and the pieces are a good size for a syrian. So you could give that as your main food and supplement with fresh treats as well as veg - eg the odd blueberry, piece of cheese or apple etc.
I wouldn't use the Bunny Dream on its own as the pieces are so teeny - syrians seem to prefer bigger pieces.
Our first Syrian had nothing but Harry Hamster plus some fresh treats, and lived to 2 years and 8 months and many hamsters have been healthy on it. Our second syrian had nothing but Rodipet and Bunny and also lived to well over 2 years old. So in terms of disease or age I don't think it makes much difference
But you do need a mix with the correct balance of protein etc, which Harry Hamster has. One advantage it does have over other mixes (other than Rodipet and Bunny) is it is sugar free and that is quite important. Sugar is not good for hamsters - they get tooth decay like the rest of us!