I'd go for DarkBASIC Professional if I were you. The language is graphically more up to date, but it's coding is very simular DarkBASIC Classic. The interface is more modern, and it's still being upgraded and developed for, while DarkBASIC Classic stopped it's development in 2002. With the exception of the one off 1.21 patch.
In relation to how hard it is compaired to Visual Basic, as has been said, it's designed specifically for games development, were the interface could be absolutely anything the user wants to create. While VisualBasic offer standard windows gadgets and forms so it's better for application work.
However, there is no reason you can't use both. Wtih DarkGDK.Net you can transfer your DarkBASIC Professional knowledge directly into Visual Basic at a later date. Plus DarkBASIC Professional, being aimed at game design, offers a range of expantion plugins allowing users to deploy more specialised features such as the Physics Processing Unit technology developed my Ageia and now being intergrated into nVidia's latest set of GPU's.
If you intention is to make a game, then I'd recommend you go for the langauge that's specifically designed to meet that task.