I have the CS6000i - I use it for a class machine. It is a great little light weight machine and easy to carry.
That being said, although I like the CS6000i for classes, I would never use it for every day sewing. The harp (for my purposes) is small. It has a nice stitch but is nowhere as easy to use as my older Pfaff with the IDT (which is a dual feed system).
The best machine for you - is one in your price range with the options that you need/want. The older mechanical machines are fantastic and are workhorses. I bought a Viking 6370 back in 1979 and my daughter now has it and it is still going strong. My requirements for piecing are needle up/down, adjustable needle position, room to work inside the harp and a variety of stitches - both the CS6000i and my Pfaff fit those needs. I purchased both my Embroidery machine (Pfaff 2170) and my piecing machine (Pfaff 2058) as well as the CS6000i off of Craigslist. Look for estate sales, moving sales etc. Great resources for used machines.
One last comment - if you end up looking at a machine at a dealer vs a big box store always remember that they will "deal" with you. They may or may not not lower the price but you can always negotiate additional feet and accessories. I never knew this until I worked for a Viking dealer. Good luck - take your time and shop shop shop!!