I think the SR Leader class takes the technical superiority crown, even if it didn't work properly
Yes that's a kettle. Anyway anorak off now.
Edit: minor bucket list item: drive a class 37.
If you're looking for innovation (as in "innovate, at any price, and upset people thoroughly with what you've done") within rail traction, chances are that Oliver Bulleid will be involved. I've traveled behind 34027 Taw Valley which is one of his, but on my bucket list is to travel behind an unmolested Merchant Navy Class engine, still in its "Spam Can" configuration. There are some in preservation that are running.
As to diesels, I'm 100% with you that the Class 37 is something very special. Was hauled by double 37s on the transport legs of a steam special 2 years ago. The sound is positively marvellous.
I've driven Swedish
T21,
T43 and
T44, as well as the shunter
V5. T4* are GE diesel-electrics, straight EMD 12-cyl 2-stroke diesel, etc. T21 were built by MAK in Germany, and is a submarine on wheels, straight 8-cyl ex-marine diesel engine, 2-speed Voith hydraulic transmission, and very, very German. V5 is a Henschel shunter, more or less.
Driving a Class 37? Well, yes, that's something I'd not turn down, not at all.