Oblivion with several hundred mods.
Vanilla Baldur's Gate was a mediocre game with too low resolution and poor monster AI. With TuTu or BGT, plus the BG 1 NPC Project and Sword Coast Strategems mods it is a brilliant game.
I haven't actually played the BG series yet! But when I do I will play the games unmoded to experience them as the developers made them.
Low resolution is not a problem for me since I usually find that games made for 640X480 resolution are better for me in that resolution (or the widescreen equivalent, 720 X 480) since I play on tiny 15,4 inches laptop monitor. When I buy a new computer with a larger monitor I'm likely going to double that. The ideal would be to get a monitor which supports twice the resolution that I want to play in so I could avoid the annoying blur I get when playing low resolution games on LCD monitors.
For those that want to play Baldurs Gate with higher resolutions but without the new content of TuTu, there is a good guide here: http://social.bioware.com/forum/Baldur039s-Gate-1-and-2/Baldur039s-Gate-General-Discussion-No-Spoilers-Allowed/Tutorial-Baldur039s-Gate-without-Tutu-or-BGT-but-with-updated-resolutions-3154080-1.html
When I have played through the games one or two times, I would likely want to try the TuTu experience, and the mods you listed seemed interesting, especially the Sword Coast Strategems. Since TuTu adds more options from BG2 thus potentially making the game easier(?), this mod seems like a nice counter and a very good addition for experienced players of the game.
I have some questions for the BG 1 NPC Project. How is the quality of writing in that mod? Does it fit into the game? Is the conversations too modern for a "medieval" fantasy game compared with that from the original Bioware game?
(I expect that the original Bioware characters have a modern way of thinking that would be unrealistic in say a historic medieval game. This is no problem at all since this is a fantasy game where this is perfectly acceptable. But I would not want to use a mod that makes the dialogue even more modern.)