My favourite combination of gluten free flours is rice flour, potato flour and tapioca flour. They don't have too strong or offensive a flavour and they work well together, particularly for baking cakes and sweet things.
Cornflour and maize flour are good ones too, and not too strong in flovour. Using cornflour and soya flour with rice flour work well in baking bread, along with one of my favourite ingredients Psyllium Husk powder
I haven't found any millet flour in my searches here in Dublin, but am interested in trying it, along with sorghum flour. Perhaps I will have to find them online.
Quinoa flour and Buckwheat flour will add their own distinctive flavours, it all depends on what you want. I don't use these flours very much, but don't let that stop you.
Everyone is different and has different tastes. I can only tell you what I like to use. I think you really need to experiment with the different flours and find what you like and what works for you. Just have fun with it!