That depends whether you like enamels or acrylics. If you like Enamels, Xtracolor is good, especially because since they're glossy, you will be able to dispense with the usual gloss overcoat before decalling. Testors Model Master paints are also good.
If you like Acrylics, both Testors and Xtracolor have a range of acrylic colours.
I mention those two brands because they're fairly widely available and they have RLM colours pre-mixed. Brands that don't have all RLM colours premixed are as follows:
Enamel:
Revell
Humbrol
Pactra
Acrylic:
Tamiya
Vallejo
Gunze Sangyo
There is a terrific pair of paint charts available at
PMS Stockholm.