I think you may have the color selection issue backwards. Vallejo has significantly more color selection than Tamiya.
Tamiya sprays great and if there were more color selection, it might be my primary acrylic. Tamiya hand brushes poorly.
Vallejo sprays fine once you learn how to do it, and it hand brushes great and is self-leveling. Vallejo isn't terribly durable and I think a clear coat is a must if you intend to ever touch your model again after it is painted. Tamiya, IMO, dries to a harder and more durable finish.
They are both fine products, IMO. I prefer Vallejo but you may not.
If you use the Vallejo Model Air line, you don't really have to thin it at all. I would suggest you use Vallejo's own flow improver, though, to reduce if not eliminate dry tip. I wouldn't recommend spraying Vallejo Model Color at all until you have more experience. It's very thick and formulated for brushing.
Have fun whichever route you go. You can try them both, you know!