[Mr B]

For me, alot of it has to do with what size line I want to use and the weight of the lure. Also how much control you need on the cast.
We have both, complete opposite ends of the spectrum out here when it comes to "cover".
One day we are Flippin' 1-5' with heavy cover, the next we are fishing no cover in 60'

6-10 lb test mono / Fluorocarbon I use on Spinning Tackle

10-20 mono / fluorocarbon I use Casting.

65 lb braid on my Frog Rod, Casting.

Split Shotting, Drop Shotting, Wacky Worming (small 4-6" worms) Shakey Heads and very small crankbaits (1/4 oz or less) get the spinning rod.

Just about everything else gets the Casting Set up.

When casting accuracy is needed it is hard to beat a Casting rod/reel as long as the bait is heavy enough to ues on it. Dont get me wrong, Spinning tackle can be accurate, especially w/ small baits but getting a 1/2 oz jig on 20 lb test into a teacup sized hole in the weeds, under a willow is much easier w/ a casting setup. I spent hours Pitching & Flipping jigs in my mom's back yard when I was a kid to get myself good before getting out on the water.

Get a good casting setup and practice it in the back yard. You wont be sorry. Start with 10-12 lb test, its easier than the heavier stuff.
Also do not go too cheap. Try to not go below $100 on the reel if you can.
A good entry level reel is the Shimano Citca. It basically replaced the older Curado. It runs about $120 and is a very nice reel.

For a casting rod, start with something in the 6.6 - 7' length in the Med - Med/Hvy action.

Let me know if you need any more info.