I don't think I 'm really qualified to answer! I used my Kenmore (straight and zig-zag) for about 25 years until the OSMG said it was shot - bought a terrible plastic cheapie for the next 10 years, and have had a Janome 2010 (inexpensive computerized) and a Bernina 750 (expensive computerized) since then. I haven't sewn leather, but I've made everything from curtains to costumes to clothes to quilts on those machines. Also reupholstered a couch.
I've started buying a few vintage machines, but mainly just for amusement. I must say, my old Bernina 830 does a terrific straight stitch, and the little Featherweight is great to take to classes and Linus.
I guess I'm saying - depends on what you want to do and how professional you want it to look! As a young mom, that was the last thing on my mind. As an old gramma, I'd like to make nice-looking quilts, hence the 750.
What do you want to make?
Cheers!
Margaret