When is it better to swim a jig vs fish a spinnerbait?

try this:        wind= spinnerbait          no wind= swim jig

Spinnerbaits definitely can have more drawing power when fish are really aggressive in clear and stained water.  I feel like spinnerbaits are a bit more weedless too.  Also, spinnerbaits are probably your better bet in stained up water.  I like to burn a spinnerbait until I reach my target then quickly give it some slack causing it to drop straight down making the skirt really flare up and the blades clank together.  No other bait can cause this much visual and audible disturbance almost instantaneously.

 

Swimjigs can be better on pressured or finicky fish.  They don't have a big wire which suggests they could be better for really clear water.  They double pretty good as a flipping jig.  They cast better. You don't have to worry about tuning them up like spinnerbaits because they won't run sideways.  You can use swimjigs to fish the same stuff as spinnerbaits, so if you're not getting a bite on a spinnerbait you can switch up to a swimjig and you'll probably get bit.  

 

You'd think a spinnerbait would be better when bass are feeding on shad close to the surface. I've found that they both are about equally effective.  If you're trying to run a bait right through a school though, spinnerbaits seem to scare the schools a lot more.  You can usually run a swimjig right over them.

 

Also what smallieking mentioned is a great point.

When the skies are clear and not overcast I generally use a swim jig over the spinnerbait. Also, when fishing extremely heavy grass I will put a swim jig on my flipping setup and swim it through grass and other heavy wood cover. I like to throw a swim jig, especially a bladed one in the summer when the bass start to key in on bluegill as well.