I would put Marui at the top. Why?
- The quality of their manufacturing is top notch and almost best in industry for standard AEG. I would only put Systema above them (which you don't have in their list). The Systema product includes both the PTW, as well as the full Systema AEG that is now discontinued.
- Almost all of their products are supported by the aftermarket.
- Engineering errors are fixed over time (you can see at least 4 revisions in their Armalite series... most other clones on the market are at most, at generation 3 of the Marui product.)
- And that leads to the final reason: almost everyone copies Tokyo Marui. Isn't that flattery enough?
KWA I would put above VFC, due to their more refined internal reliability
Umarex is NOT a manufacturing company. They are simply a trademark licensee. For example, the "Umarex MP5 GBBR" is actually manufactured by VFC. Or, the Umarex MP5 AEG is manufactured by G&G. They only hold a license to the HK trademark and logo, and sells that license to manufacturing companies, in exchange for use of the HK logos and markings, as well as the Umarex name plastered on the product.
GHK I would not consider to be high end... I'd actually put them below ICS, simply due to the low reliability of their guns and magazines. The only thing they have going for them, is original engineering.
Like Forever_kaos and Kozzie has mentioned, this is all relative, and a lot of this comes down to personal preference and experience. Qualities that I look for in a company may not apply to other people.