Best HO Steam Locomotive on the Market - Model Railroader Magazine

It is a toss-up, for me, between my Lionel Challenger in HO and the Trix Mikado.  I agree with the poster who feels that his P2K 0-6-0 is a little gem.  I would bet that the P2K Heritage series are all excellent runners and are especially finely detailed.  The smaller one are light, though, and I have heard similar complaints about the larger engines in that series...they don't rank among the best pullers.

So, I find that, for availability, service, and for overall quality, it is a generally safe bet with the Broadway Limted Imports model trains. They can be had for bargain prices well below the MSRP, so they are competitive against other manufacturers in that regard.  I have been happy with BLI generally, although my first loco, the J1 Hudson still has its original QSI decoder where the chuff rate maxes out at about a scale speed of 35-40 mph, and is long since out of synch.

Finally, it would not be right to leave Bachmann Spectrum steamers out of the discussion because at least one of them is a marvelous item, and that is their 2-8-0 Consolidation.  Not getting into fidelity across railroads (I wouldn't know anyway), they look great and run great...lots of fans.  I suspect their 2-6-6-2 is good as well, and perhaps their Mountain.

You have to find what appeals to you, go for the higher end stuff to be sure of better performance (on a sliding scale), and count on good repair or replacement service from all of them.  Not Lionel, though, they are out of HO production.