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There are two types of skin shapes, straight or cut. I use skins that I've cut, cutting skins is easy enough g3 skins comes with a skin cutter tool and there are numerous videos online if you don't already know how to. Alternatively you could use straight skins which you would try to match to the mid width of your ski, straight skins require no cutting, but as mentioned above they don't provide as much grip. With regards to the brand, I personally use g3 skins the adjustable tip 'arms' and the tail clip works well I rarely have problems with the tail clip flicking off. BD skins don't work so well if you have large square tips you either have to sand your tips so they are rounded or buy the larger tip loops.
Hope this helps, if you've got any more questions just pm me and if you tell us what skis you have then I can find the size you need