Like J.C. said, hand painting would yield excellent results from a talented artist. It's somewhat more versatile than vinyl, you can continue a line/pattern around hard edges, welds, and angles. But, it's harder to get the same pattern/lettering consistently, or to achieve a perfect symmetry between sides. Depends on your art level/hand steadiness/patience.
Stickers have good sides though. Fast to apply. Durable yet easily removed. Very consistent when doing multiple drawings, crisp edges, and straight lines. For permanent and long-lasting results, paint the bike, apply the stickers then spray a clearcoat all over.
I think a mix of both methods is the best alternative. Paint for lines (pinstriping), shapes, solid colors... Stickers for lettering, logos.