I agree with everything John C said, but it seems directed at someone who already knows he/she wants to build a model railroad of some sort and not just someone who might not want to go further than a Christmas tree circle. I don't regret buying the set I did, but I was disappointed with the track it included. It was RealTrax, but my impression would have been the same had it been FasTrack or the stuff that came with my American Flyer set 60 years ago. My mistake was adding pieces at the time of purchase instead of waiting. Fortunately, I didn't add that much, so it was only a fairly small waste of money and satisfied me through 3 Christmas seasons, so I guess it really wasn't a waste after all.
I don't remember now what drew me to MTH, but once I saw it in my LHS, new at the time, I was hooked. I'm not drawn to any particular road, era or operation. I'm going to have 4, maybe 5 engines, period. One will be Old West style passenger 4-4-0, a couple of diesels (Veteran's SD70 for one), my Christmas passenger 4-6-0 and maybe a 3rd diesel. My goal was to have at least 1 steamer for the smoke, but diesels will be the main runners. Like my clothes, I don't care what matches. If I like a boxcar, I'll put it on the track. I don't care if they go around in circles, I just want an over/under feature with a bridge and the ability for 3 trains to run unattended with me controlling a 4th. They will all be RailKing rated for O31, so they will run on any brand track and any layout (except O27 I guess). If I decide to pursue a garage layout at some point, then I'll revisit the number of engines, etc.
Slayers, I don't think you can really go wrong with any set sold today, just give some thought to what will look nice under the tree for years to come and what will lend itself to expansion. The passenger set I bought is pretty limited. I have all the cars for it, so it's done. The coloring is Christmas, so it's somewhat limited to the holidays. If you don't really care all that much about smoke, then get a nice diesel set. Check to see if there are any clubs around. I don't know where in MI you live, but there should be something where you could maybe take a day trip. Even if it's not O gauge, someone might be able to give you a reference. If you get an MTH set, be advised that you will not be able to use all the engine features unless you upgrade to the full DCS remote. The advantage to buying a set is that it comes with everything you need. I don't know if I could have saved money buying everything individually. I'm not even sure I could have bought the engine separately. The only piece I really don't use is the remote because I upgraded within the month.