I would use rebar over wire mesh. Wire mesh can stretch and pull some, rebar will prevent a slag, if it cracks from dropping lower than the other slab. You can see this in a lot of older places where the slab has cracked and dropped.
With that being said, I didn't have rebar in my garage slab, but rebar was required in the footer. I had control joint sawed into my slab and they did exactly what they were intended to do, control the crack. In each control joint you can see where the concrete crack in it. ANd a garage is going to be a little different that your concrete that is outside. Any concrete that you pour outside, I highly recommend rebar. And if you make pours later, you want to pin to existing concrete.
All of y sidewalks, and we have then completely around the house and from the house to the garage, all have rebar in them and the rebar is overlapped at the control joints. This keeps one slab from dropping and making a trip hazard. Something that you definitely don't want to have. The first sidewalk I poured was maybe 10 years ago and maybe a little longer. I took out the sod and put a good base of gravel down. The gravel was down for over a year and was drove over by the garden tractor and walked on many times. That sidewalk has control joints in it at every five feet and has never cracked in any one of the joints. The other sidewalks that were put down, never got the compaction that they should have had, and a few of them have cracks in the control joints.
But most of all, the key to having a good pour is starting out with a good base. The tighter you can compact your base stone the better. Rent a plate tamper for a weekend. Spread some stone a few inches thick at a time. Tamp it in over and over. Then add a few inches more of stone. Tamp it in over and over, and wet it down if it is dry. If you don't compact the stone, it will compact some when the concrete is poured, and it will compact some more after the concrete is cured. If you don't have a block with a ledge on the outside, you can see where the concrete guys will strike a line, and a year later, you can see where the concrete has settled down some. So good base prep is a must.
And if you can't swing the cost of rebar for the complete floor, try swinging enough cost to rebar across the areas where you will have your control joints cut in. That way when it cracks in the joint cuts, it won't let ones portion of the slab drop from the other.
