Best steam railways in Wales

[TheOGCCL]

We are thinking of visiting Wales this summer and enjoy going on steam trains of which there seem to be plenty to choose from.

What are your picks for the best steam railways in Wales and can you suggest an itinerary (start point is London) that doesn't involve having a car? We would normally be away no more than a week.

I'd say Ffestiniog and/or Welsh Highland Railway is the "best".

It's quite accessible for those without a car (multiple connections with the "big" railway), and is a decent length of line, varied, etc., with route options (i.e. ffestiniog only, WHR only, or a combo full length of both).

WHR runs from Carnarvon to Porthmadog and Ffestiniog runs Porthmadog to Blaneau Ffestiniog.

I haven't done this one personally but have driven the route its very nice, Friends have been on it and enjoyed it, if you have seen Hinterland crime series on Netflix some of it is filmed in the area
https://www.rheidolrailway.co.uk/

The trains are not the easiest from London as they involve changing either at Birmingham or Crewe.
Aberystwyth, Porthmadog or Llandudno are your best to check out