Welcome to tbynet--you've come to the right place. This is kind of a hard question to answer, beyond generalities like what Mark mentioned above. Basially tym=Mahindra and Branson=Century, with some exceptions as far as attachments are concerned. It would help to know what your planned uses are and perhaps to have some more specific questions. I, and everyone else on tbynet that I know of, would second Mark's comments about the dealer--go to all the dealers and drive all the tractors. That should help narrow things down a bit. All are good units and good values. Price can vary a lot regionally so you really need to get serious quotes from your dealers and not go by what you may find on the net. What's cheaper in Central Virginia may be more expensive in Massachusetts.
As for the differences between the 2 lines, Branson/Century do not yet offer as extensive a line as Mahindra, which makes compacts and utilities. Not all Mahindra tractors have TYM equivalents. This is because they are not all made in Korea--some are made in India. Another difference is that B/C do not offer hydrostatic transmissions yet--synchro shuttle is what comes standard. I think B/C have a few more standard bells and whistles but Mahindra/TYM offer more options.
I think these lines are fairly equivalent when looking at value and performance in the 28-45 hp range. If you want bigger or smaller, B/C are not offering these yet, though I hear the larger units are in the pipeline.
This means, as mentioned earlier, it boils down to 1) dealer 2) price 3) your personal taste. I suppose 2 and 3 could be reversed depending on your budget and how much of a difference there is. Of course the first step is to assess your needs, which we can't do until we know more about your land and what you want to do with the tractor. Fill us in!