I went with SieMatic and HATED IT! They claim to have great quality, but their QA is terrible, and when they make mistakes rather than owning up to them they stonewall. I ordered a kitchen, they put in the wrong one and it took me 2.5 months to get them to come look as they insisted it was correct without even seeing it. Then when they finally replaced it, they didn't spray all the new panels the same colour so I now have a patchwork mishmash of colours and they're refusing to fix.
For the money, unless you have a very high tolerance for pain, stay away--go with a provider that stands behind their work, when they make a mistake they own up to it and they are good to work with. SieMatic is not cheap---I regret every second that I chose them, as now every day I have to look at multiple colours of panels on one kitchen.
I have a friend who went with Harvey Jones and loved it---our experiences were polar opposite. They were responsive, responsible, respectful and made a stressful situation very easy. My experience with SieMatic was as bad as it can be.