This is pretty subjective, there are trains that sound fine and like the real thing yet there are sounds mods available and probably more to come. That being said here are some locos that I think sounds pretty good: Class 20, Br 425, Br 101 Expert, Class 465 to name a few
This is a tough one, because there are some good AP sounds in some british locos, like the 465. however, in my personal opinon, the Expert 101, and Class 87 sound the most accurate to me in the game. however, there are sound mods you can get, so there's more additions to the list above
Basically most of the UK classic diesels, possible exception being the Class 33 which sounds a bit naff to me. The BPO Class 47 stands out as does the original NTP Class 45. The SHG VP185 rework of the HST on MML is also very good, especially now you can run with the cab doors open. The SHG Class 158 is very good and to my ears the Scottish version had a slight sound buff.
The 323 and 465 sound very good to my ears, like the real thing. The 31, 40 and the 47 also sound very good. I would say for me if I had to pick one, the 323 is the most realistic in my opinion.
The Skyhook HST sounds very life-like, I just wish the end power car was louder when on full power as it was in real life.
The HST, all Electrostars, the 465, 700 (and the other Desiros as they all sound similar), 801, all BR classic diesels, the 66, 390. The 170 sounds are also accurate. The Pacer and 08 also have accurate sounds. I also like the sounds of the TGV. Before anyone comes along and says they're not accurate or that I'm wrong: I spend my working life on 170s and have a good idea on their sounds (pain in the rear to clean, especially on a Saturday night). see and hear 66s every time I go to/from work. I also hear the 801s regularly, and videos I've seen of the Desiros sound the same as in TSW. Sounds overall are subjective anyway.
Another vote for the 323. It helps that it’s a unique sound, and tinged with nostalgia (for me). The 66 also sounds decent, but I’m not sure which version is better!
That can be a problem since there's a lot of them, just like the 47s. Although the 47s in particular seem to have different horns? Do they have different horns on different versions in real life? Engine sounds seem good compared to videos I've seen. Never had the chance to see a 47 or 66 in real life, just vids. I can vouch for the GP9 and GP38 on Oakville. Those are spot on.
