BGT & Tutu are amazing projects, but:
BG w/Tutu or as a part of BGT provides a different game experience than standard BG. Certain game functions, spells, abilities, etc. introduced in the sequel are applied to the original during the conversion to the newer version of the engine. For example: kits were not available in BG. This backwards application of gameplay changes is not necessarily a bad thing, but those who have never played BG before should be aware that the conversion offered by these projects is not limited to a graphical upgrade.
I recommend playing at least some of BG in its unaltered form if you would like a more original experience of the game.
Then you can play it again with BGT or Tutu. ;-)
That's more or less what the conservative guide is for.