MTH RailKing and Premier engines and rolling stock and accessories. IMHO, MTH offers the best 'bang for your buck' available today. Starter sets are a great value also. They also seem to offer more in the main road name I want, BNSF.
Lionel Also has some great products and features. I finally got my 1st Lionel diesel early last fall and can't wait to run it. 1st BNSF diesel they have had that I wanted and could afford since re-joining the hobby. I think they have the best sounds. I also really like Lionel Fastrack, great system, well thought out. I went with Atlas because of noise, but plan on having some Fastrack set up somewhere someday. I think they also have the best power supplies, I am using the Powerhouse 180's and would love to have a ZW-L someday.
Command Control is what got me back into the hobby a couple years ago, started with MTH starter set and DCS system. I have a Legacy system on order, looking forward to getting it and trying it out. I also like all the electronic stuff you can do with your train control and accessories.
Atlas track & switches. Atlas also makes some fine diesels and rolling stock as well as other items. Their signal system is on my 'must get' list. I think they also have nice accessory building kits, etc. Don't have much yet, but they are on the list of things to get in the future.
Added: Forgot Ameri-Town buildings and layout wire from our forum providers, OGR! Also very nice stuff!
To OGR: If anyone from OGR reads this, any chance of getting #18 & #20 - 2 conductor and #18-20-22 - 4 conductor in this same type of wire. (Possibly with a different color outer jacket, if not gray is fine) I would purchase some as soon as it's available!
Everything else I forgot to mention. I have had very few problems with anything from any of our train or accessory manufacturers. The couple of minor problems I have had were self inflicted, not the fault of the broken piece.