After some further research my conclusion now is to go with the Gossen Starlight. Some considerations: it is small, light, has a special zone system mode and as a bonus does footcandle, lux and other intensity measurements. Only disadvantage, it's the most expensive of the three.
For whom it interests, I have made a comparision chart on this link: http://spreadsheets.google.com/ccc?k...YOGRQdmc&hl=en
Thanks to everybody. Further comment welcome!
The Kenko KFM 2100 has a backlit spot-meter reading only, the main panel on the body Isn't backlit, but it doesn't matter because it remembers the last reading and you can use a torch if it's too dark to see it.