Williams makes a great product for the money you spend, usually less than other brands and Williams has all metal gears unlike any other company! I have several Williams and will buy more as finances allow. For your info Williams does not come with TMCC or DCS command control, you must add that yourself.
Like Jim I have the 671 S2 steamer and really like that locomotive, very powerful and has smoke & whistling tender with bell feature also. You will not find as good a quality as Williams for the price even with the other companies like Lionel or MTH or Atlas.
Atlas from what I have heard has good quality as well but is almost twice the price of a Williams engine, also Atlas can come with TMCC installed for an extra cost.
K-Line is now made by Lionel so I have no experiance with current K-Line products. If you can find older K-Line in the box you may get a good deal on it.
Lionel and MTH do not always use metal gears and the gears can tear up easier than a Williams if you load down the engine with a string of frieght cars.
Also there is Weaver trains, I must be nuetral about quality as I don't own any Weaver engines. I have a few Weaver frieght cars that have coupler problems when using with Lionel style couplers.
Then there is RMT or Ready Made Toys that make semi-scale stuff or midget O gauge in the case of Beeps & Peeps as they like to call their engines. Some of the guys on here really like the RMT trains. I have the RDC or rail diesel car(passenger car) and it runs good, so far no complaints with it.
Last company that I know of or have heard of is SMT, seen their add in CTT mag, that is all I know on them.
Lee F.