I tried Cura, I tried Slic3r, I tried the Prusa version of Slic3r. Then I bit the bullet and bought Simplify3D, yup it's worth the money.
While I was waiting for my first printer to arrive , never did but that's another story, I played around with various free slicing and printer simulation software packages.
When I tried using Cura, my biggest issue with it was generating supports, it would miss areas that needed support and try printing in mid air. That works for bridging, but trying to START printing in mid air just doesn't work.
For the money that you spend on it, nadda-zip-zilch, Slic3r is a great product and I think the Prusa version of Slic3r is even better. I used them for a couple of years but...
I found that if Slic3r cannot fit a complete perimeter pass into an area it will leave it empty. Think about printing a wall that's less than 1.5mm thick, you'll get an air gap. During the build that may be OK, it'll be weak, but hidden. On the final layer that's not a good thing. Simplify3D gives you the option of filling these areas in the perimeter with either a single pass or solid fill. I made the mistake of trying the solid fill option, ONCE. Watching the printer try to do a solid fill on a 0.5mm gap for 15-20mm convinced me I didn't want to try that again, didn't think the printer would survive the shaking.
Simplify3D also lets you do things like changing speeds, layer height, temperatures, etc. during the print. To do that with Slic3r or Cura you need to slice the model various times, then find and stitch together the appropriate parts of the gcode files. It can be done, but it's a hassle.
If you're just starting out in 3D printing Simplify3D is probably not worth the investment at that time, you've got too many other things to figure out, how to get the first layer stuck to the print bed, what is acceptable print quality to you, how fast can your machine print before the quality turns to crap - minor stuff like that. However if you've been printing for a while and want to increase your print quality, then Simplify3D is worth it.
Don