Hi,
It really depends upon what kind of shooting you do.
If you look over your electronic albums and see what photos you like taking and want to keep taking, check the EXIF data and what the lens ranges are. You can, with some of the software, check the data base to see where the lens ranges are.
That should help you decide where you should spend the most of your money.
Unless you expect to deposit money into a fat account, I'd recommend caution on expensive fast lenses in the f1.4 and faster lenses. The cost goes up pretty dramatically, and the bokeh is nice, but I'd argue that it isn't twice as nice at twice the price (unless someone else is paying for it - such as an employer or your ongoing and steady customers). The f-stop difference between f1.4 and f1.8 isn't significant, IMHO, to warrant the cost.
On sharpness, I'm not sure that there's a great deal to be gained with a prime over a zoom either - although I favor prime lenses, I'm likely a creature of habit, even though I embraced digital technology early on, I still use lenses from that pre-date sensor technology.
Zooms are handy for composition, and the sharpness difference between a modern zoom and an average prime is likely trivial. What should drive the train is this: it would probably be better to pick something that suits you than worry about sharpness.
Finally, I would suggest that you try to stay in a 'fast-ish' range, and consistent aperture, if your pocketbook allows it. F2.8 is great, but dear, and for me, a heavy SOB, probably the key reason for my affair with primes, they are lighter and faster.
You'll also find that faster lenses will be easier to focus (both manually and automatically).
Good luck on which ever choice you make and as always, my best,
Mike
