TOKELLY posted:Bob, what differences are you seeing between the Challenger and the Y3a? I own both, and the chief differences I've noticed are: 1) the Y3a can run on AC, DC, or Legacy while the Challenger is only AC or Legacy; (on straight DC the tender reverse light is illuminated going forward and off when going in reverse); 2) the Challenger had some problems backing through American Models switches until I switched around two wheelsets on the tender; no problems at all with the Y3a; and 3) the Challenger was missing some simple details, such as an ash wheel on the engineer's side. I know there are some design improvements in the Y3a drive coupling that Carl Tuveson pointed out in his review, but those may not be noticeable until the Challenger begins to wear sooner. Are there some other differences I may have missed?
You have captured most of the differences. The Legacy speed step programming is more evenly progressive in the Y3a, yielding slower speed capabilities and smoother more realistic starts. There are more Legacy sound goodies and the extendable tender tether is a big plus. The Y3a is just a better model and its build quality is superior. Another desirable attribute is that it is an articulated steamer that is no larger than the Gilbert Northern which leads to the Y3a sitting and running better on Gilbert curves. I like the sound of the whistle more, too.
I own and enjoy running examples of all of the modern Legacy L-AF diesel-electrics which are excellent. However, a truly great steam engine beats a diesel any day. 
Have fun.
Bob
