Upload & Sell: On
Not sure about your question: "which one do you reckon first?"
If you are chosing a macro lens, I would lean towards the Canon for resale value. I have had two, both purchased used (about $400-450 USD). No real loss in value if they are well cared for. The Sigma used market may not be quite as solid but the lens is supposed to be excellent.
Lighting is a whole 'nother issue for macro. You need tons. Or some flash. Or fancy stuff like a ringflash or two flash sources. Now its getting pricey. If you dont have a flash yet, concentrate on the basics.
Maybe a macro lens if you anticipate a lot of shooting macro. Otherwise, play with the 70-200, a great lens. Get a flash. Maybe a used Canon 400 or 500 series.
See if you can borrow a macro lens to see what's involved in true macro where you have extremely shallow DOF even with a lot of light and stopped down.
Do you have other lenses? If not, many would suggest a 50 mm first, like the Canon 1.8 or, more pricey, better build, the Canon 1.4. I'm not up on it, but you can reverse these lenses for macro work.
Finally, if you want to print the reworks, as Doug indicated, you need a large file with the adjustments applied by you (or someone else).