Any good suggestions on a modern diesel such as a Dash 8 or 9.
Which gauge? I think I read that you are looking into N gauge.
The answers can be totally different depending on gauge. Kato probably the best with N if they make one.
Question answered on if they make one.
Kato in N and HO-if available for dash 9
If you are working in N scale, Kato has made Dash 9’s, AC4400CW’s, and is currently releasing both ES44AC’s and SD70ACe’s. I know Katos are very smooth running locos, but not always the best detail. You can look for yourself. If you’re looking for modern GEVOs, your other N scale option is Fox Valley Models. They have and are still releasing both ES44AC and ES44DC models. I know very little about this company, so I can’t make any recommendations.
Athearn also makes SD70M, SD70I, and SD75I locomotives in N scale. During my brief experiment with N scale, I had an Athearn SD75I and quite liked it. Good looking, and ran reasonably well.
In terms of Dash 8s, Atlas has made a Dash 8-40B, Dash 8-40BW, Dash 8-40C, and Dash 8-40CW model in N. They also just announced a new run of Dash 8-40C and Dash 8-40CW models, due in August. I know Atlas locomotives are known for running well, and the detail is very nice.
Hope that helps!