Hello Aryforce,
I just wanted to add my two cents to the discussion. There is a package available called Trainz Railwayz which includes both Trainz Classics 1 & 2 and TRS2006.
If you do not plan to download older assets (that is only download assets that are designed to work on TC 1 and/or 2) then TC is definitly the way to go. I have been extremely happy with my copy of TC. I am running an "older" HP PC running and AMD athlon64 3200+ @ 800Mhz with 1gb of ram, DX9.0c and a Radion X1650 video with 512MB ram @ 1680 x 1050 res. and have excellent results.
However, TRS2006 does not work as well. I always have stutter on this system. I realize I need an upgrade but I can not do so for several years to come. CMP provides the never clearing "updating database" screen about 75% of the time and used to drive me absolutely nuts but if you know for sure you have not made any changes that require the database to be updated, you can simply press the escape while the message window is active and it will go away and not trouble you further. Another minor annoyance with 06 cmp is I have to completely exit cmp then restart in order to access the game instead of clicking on the 2006 icon at the top of the cmp screen. If you want content though, this is the best platform!
If you go the TC route, and you plan to download none-TC content - particularly content that uses built-in assets such as locomotives and rollingstock or even some industries and others, you will have to have 2006 available so that you can import the built-in content from that platform to make it work in TC. Now having said this, you should know that I have downloaded the DHR and have it working beyound my wildest imaginings. Yes, I did have to do a bit of importing to get some assets to work - this is to be expected with none TC content - so be for-warned.
As for the up-coming and much anticipated TC3 - only time will tell if Auran releases it without the legacy content. I would expect them to do so since the release is actually targetted at improvements and to include the old content could introduce could be detrimental.
Of course, if Auran does include the older content, I will guarantee that we will be getting people who will fill the forums with complaints that the old content "does not function as it should". On the otherhand, if it is not included, you will get all those other complaints that "content is broken" or "my downloads don't work". A catch 22 situation if ever there one.
Lastly, as the product is maturing, we as content creators will be moving to create for the platform that we personally own. As for myself, once I get back on feet after chemo, I will be focusing my efforts mainly on TC products, though a handful of items will be produced for 04/06 as I have promised these previously.
Good luck with your choice. No matter which product you choose, once you recognize the limitations, you will find that you have the greatest product on earth!
Have fun!
Brian