You'll find that most highly experimental engines from anywhere draw bad reactions.
It's interesting just how different we are. I count J3s, S1s, L4s and A2s all among the most attractive.
This I can agree on. The worst offenders on this aren't American; the loading gauge in steam days wasn't high enough. Some classes of Russian 2-10-0 had so much airspace under the boiler you could almost walk through.
For me, solid or footboard pilots look best. Cowcatcher-style pilots are alright if they don't extend too far. The most consistently ugly are pilots made of horizontal slats; these tend to ruin Argentine, Uruguayan and Paraguayan steam.
Most British and Italian steam looks too... well, clean, and I particularly don't like most British smokeboxes. German and French steam somehow looks finely engineered.
I tend to prefer semistreamlined steam to fully streamlined. I like, for example, CP steam with recessed headlights - the barely-streamlined Royal Hudsons and Selkirks, but actually more so their late heavy 4-6-2s and 2-8-2s which weren't even rounded off. Skyline casings are another weakness; favorites here are unstreamlined SP GS-series and AC-9s and East German 01.5s. Among unambiguously streamlined steam, those that still don't try to hide the shape (NYC Hudsons, N&W Js) come off much better than earlier shrouded efforts. In fact, it's questionable which are worst: the ugliest messy engines, or the most strained efforts to hide them.
EDIT: Just remembered what I was trying to, an example of what I'm talking about. DRG class 05 4-6-4s. The shroud made them unrecognizable as locomotives. I hate when streamlining hides the wheels.
