The fastest trainers I've had, by far, are Token Young players from the Youth Academy, specially when their market value is high. Nordeus generated players are fast trainers, but not as fast as Young Players; I think it is has to do with the quality; NGE are 5 * (I mean, I never buy a less than 5 * player), while Young players are 4 * max. I guess the less stars a player has, the faster he trains.

In my experience, market value (combined with stars) and fast training are strongly related, but not always...

Cholo