Definitely fitted T's - strong preference. They always make me look like I have some curves! In contrast a basic T makes me look like a flat-chested stick figure.
But, the pics you showed have v. high necklines, at least it looks that way. While I am not someone who would ever wear a plunging neckline (modesty, and lack of good cleavage), I think a slightly lower neckline would be better than what you have in your pics. Like, enough room that a circular style of necklace would be lying mostly on skin not on T-shirt. Or a modest V-neckline. But the necklines don't need to go right up to the base of the neck like it seems to on the photo. It's not as fashionable, and it limits how you can accessorize it with necklace choices, etc.