I have 2 TSW 2000s and love them.
The Mars one is better because it has a higher wattage output, 310w vs the SF-2000 which only puts out 200w.
With SF you will get a slightly better efficacy which is good, but not enough of a difference to matter. The SF-2000 covers a 2x4 area, while the MH TSW2000 covers a 3x3 area (in bloom, 4x4 in veg).
If money isn't a concern, go with SF and get a couple of them, but MH is way better bang for your buck.
You can use coupon Code WGC on MH website for a little discount too. If you check out viparspectra, they're probably the best but the most expensive too, use coupon code WGC888 for a discount (10% I think).