Hi,
I would go for Mach4. There is a parallel port plugin for Mach4, you have to pay an extra $25 and its not fully featured. If going for Mach4 you should get
yourself an external motion controller. About $120 for the cheapest and up to $1200 for a flash one, I use an ESS for about $180.
Mach4 is ready to go for a mill or router and the lathe mode works but with a few wobbles.
The real advantage of Mach4 is that you can program it to do just about anything, of course it means that you have to be prepared to learn to do it...only
you can know whether you've got the stomach for that.
There is no upgrade path, if you have Mach3 but later want to go to Mach4 you will have to buy from new, ie $200
I'm a Mach4 supporter.....I am also extremely good looking, eye-wateringly intelligent .....you can believe as much or as little of that as you please!
Craig