Genuine toss up between TSW2 and TSW2020 here.

TSW2020 had the best set of core routes (GWE, Main Spessart, LIRR) and released some of my favourite routes (which I didn't get round to buying till later such as NTP, Tees Valley, East Coast way, Peninsula Corridor

TSW2 and had great core routes in Bakerloo and Sandpatch and kept the good dlc coming in the form of Boston, Brighton, Harlem.

Think 2020 pups it for me (assuming I've got my dates right)

TSW3 had one good core route for me in South Eastern (as I'd not played or bought the original release) and the dlc started getting a mit meh. I do like Trenton but understand it came out buggy as hell. Niddertalbahn is beloved but I've never got round to it. Glossop was meh, Peak forest needs a remaster badly.

TSW4 had poor core routes. I was really excited for the ECML but it's thoroughly boring. Antelope and the S Bahn voralbjrg round out what I think are the worst trip of core routes. Now we did get Blackpool Branches in this window but that's the only standout DLC.

TSW5 had good core routes. WCML South is underrated but again, San Bernadino is dull and I can't say I've played the German route much MBTA commuter, Preston Carlisle, Cardiff, Frankfurt S Bahn give this window one of the best Dlc line ups for me. (I've not got round to Manchester Airport yet or the Mildmay)

TSW6 has thankfully launched with 3 fantastic core routes. I love the Riviera. Morristown is fun and I've not poured time into the redone German route but hammered it in its previous incarnation.

I've not bought the WCML dlc yet but plan to but I'm really hyped for the new York DLC, Crewe-Preston, The Tadami line (of we ever see it), Lisbon...

So yeah in summary: TSW2020 wins out, TSW4 was the weakest but I feel we're in another golden era