It depends on your viewpoint: is painting miniatures a craft or art? If you're just interested in getting figures onto the tabletop, decals make life so much easier. However, if you're aiming for that bit of individuality and sensation, there's no better way than custom freehands which, of course, need a lot more practice, effort and time.
Personally, I go for both as required. It's a nice little challenge to research or make up suitable motifs and then get them onto the actual model (which often needs a fair bit of artistic license). But there's a level of detail and accuracy I'm neither able nor determined to achieve, and for that – and a uniformed look in particular – I'm happily using decals. Quite often I find myself mixing both approaches, that is painting over decals, copying given designs by hand or throwing together decals and freehands in the same unit/force.
Whatever works for you best is the right choice.
