Wait
GHK are releasing probably the best G17 later this year.
If you must buy now, VFC/Umarex is very expensive ONLY because of the trades, the gun is fairly poor.
The dedicated CO2 version is only half blow back, and absolute shite.
CO2 mags that are designed to be used with the normal gas version will destroy it.
KWA is a solid option, but old technology. I wasn’t aware they made a CO2 capable version. New version do not ha e any trades, finding an old one with trades in decent condition will be tricky