We have the SWF 1501c and it runs 12 hours a day, 4-6 days a week for the lat 18 months since we bought it without complaint. I would not get the MA-6, go with the 901c if you are serious but money is an issue, otherwise go with the 1501c.
Keep in mind you be hard pressed to make a good $/hr with a single head on large stitch count jobs. You might want to look into a multi head like the 1504 Dream Machine
SWF MESA Distributors, Inc. | SWF / E-UH1508D Embroidery Machine. This sucker cooks! It runs around $30K but the payback should be pretty quick on it.
Some other notes,
Stay away from multi-function machines.
Make sure you visit the vendor with your artwork and have them run it on their machine for you.
You will need to get more accessories than come with the machine, look for hooping assitants like the hoopmaster, quick change hoops like fast frames, and a good supplier of consumables.