With the issue of Steam vs Diesel, I feel that with the Diesels, they tend to be seen as villianous with the likes of Diesel, The 'Bowled Out' Diesel, Arry and Bert, Diesel 10 and Splatter and Dodge. As much as I like these diesels, despite them being bad, I also find that there are the good diesels likes Boco, Daisy, Salty and of course Rusty. With the Steam Engines, most of them are good, with the exception of Spencer who is seen as the bad egg of the steamies. Overall, my preference would be the steam engines.