If the Berninas are close in price, I would definitely recommend the 200. The 200 is newer and can be updated to a 730 so I would check to see if it has this update. If so, it would be able to use the BSR, otherwise neither one of them would be. With the 200, Bernina changed the embroidery system. 160, 170, 180 use the older system. The 200 used the same modual and hoops used on the later models. The embroidery is built in so you can use it stand alone, if it has the Bernina software, you do need a dongle for it to operate on your computer. Also, the current version of the software is 7, versions older than 5 are no longer supported and won't run on newer operating systems (beyond Windows XP). If it has the update, it can take a USB stick, otherwise it takes Bernina specific cards, but you can use a box to put designs onto a blank card to transfer to the machine.
If the seller has everything for embroidery for the 180, it may work just fine for you but just the learning curve could be frustrating since it won't take most of the newer accessories they have come out with since.
Look at the back of the machine and check the serial number. The first digit of the serial number indicates the decade it was build, starting with 1= 70s, 2=80s, 3=90s, 4=00s, 5=0x. The second number of the serial number indicates the year within the decade, so 45xxxxxxx would = 2005. Remember that these are "Sewing Computers" that have computer boards, Also, I think the 200 and 730 are both windows-based software inside. It would be important that either machine you would choose would have had regular service at the Bernina dealer so ask when it was last serviced.
I would also check out used prices on ebay - will give you an idea of market value. I won't guess since I have not been watching used prices. If you belong to Yahoo, you can join the "sewitsforsale" group, where a lot of people sell machines and sewing-related items, and search ads for recent Bernina listings. I will add that I have a Bernina 440 with embroidery that I bought used in 2006 and still love today.