CSS editing? whats best? external file or hikashop

Hi,

It depends on what you want to do.

With template CSS, you can only add new css rule. You will override by addition (or replacement).
With hikaShop custom css, you can add, modify and remove some existing rules. You custom css will change change with updates which have the effect to not have the new CSS rules of the default hikashop file.

You can have a sort of mix with css import, if your custom css just contains:

@import url('frontend_default.css');