If you mean the new “soft” ones that cost around £55 I went for the 12 tube but I carry a lot of pole and top kits – I have the rive 9 tube hardcase previously and it simply wasnt big enough.
In the preston I carry two 13m poles; 3 extensions and up to 4 tubes of top kits – 3 oval colmic ones and a 5″ black type. Can also fit in a brolly if needed, feeder arm, Rive roost and half but extension.
You need to think about what u may carry, personally I always err on the bigger size as even if you only need loads of kits occasionally it not great if it wont fit in the holdall!