While on the software department I don't believe there is a difference in free and paid, hardware however do make a big difference in production. For a long time my stuff were badly mixed due to poor choice of headset, I used a pair of old Sony headset not designed for production, only until @Soundchris recommended the ATH-M50x to me and my production improved twenty-fold.
What are your hardware that improved your production greatly? Prices don't really matter.
Focusrite Scarlett 2i2 + two Samson R21S mics.
The former opened up to me actual plug-and-play when it came to all my stringed instruments; the latter upped my recording quality for both voice and percussion. Also, I could move the mics wherever I wanted to create different sorts of stereo effects since my mic signal is basically mono left mic + mono right mic.
The R21S, as I have said in the past, is the poor man's Shure SM58; its quality is that clear. The drawback is that compared to the SM58, it is rather fragile.
A pair of KRK RP 5 G2 and a Behringer UCA222.
My Roland Octacapture, my M-Audio BX5d's, a proper Fender Telecaster and my Mustang GT200. You have to spend the money on the gear, no doubt. Probably the biggest improvements in quality are achieved from quality gear.
