Newer Clients are definitely starting to get more usage. More things can be done with them now, tons of new items/monsters/areas/mounts. If you are looking to get creative, continue on your 1.0 project; if you want to make a server to have nostalgic memories then go for 7.4-7.72. Otherwise, 8.6, latest client or completely custom client.
Regards,
Extrodus