You can tell a good bathtub from a bad one before you even get in, just by looking at the edge of it. A good one has a lip wide enough to set down a glass of water without thinking about it, sides that hold heat instead of bleeding it into the room, and a drain that doesn't look like it was added as an afterthought. A bad one is cold to the touch within ten minutes, scuffs if you look at it wrong, and makes a hollow, cheap sound when the water hits it. That sound tells you everything.
If you're starting from nothing, go with a standard alcove tub and a shower combination before you chase anything fancier. It's the one that works in the most bathrooms, fits the most budgets, and doesn't box you into a layout you'll regret when you sell the place or just get sick of it. Freestanding tubs look wonderful in photos, but they need floor space most of us don't have and they're a pain to clean around on all four sides. Get the basics right first. You can always add the soaking tub in the primary bath later, once you know the house and know what you actually use.
On color, white and off white still win, and not because I lack imagination. A white tub reflects whatever light is in the room, morning or evening, and it doesn't date the way a colored tub from the seventies dates, which my aunt's avocado green tub in her old house proved for forty years straight. If you want warmth, bring it in through the tile or the surround, not the tub itself. Matte black fixtures against a white tub look sharp in the morning and almost moody by lamp light at night, which is a nice trick for a small bathroom that doesn't get much natural light to begin with.
What separates a tub that lasts from one that cracks by year three comes down to what's under the surface. Cast iron with enamel holds heat and takes a beating, but it's heavy, so check the floor can take it before you fall in love with one. Acrylic is lighter, warmer underfoot, and forgiving if something gets dropped in it, though a thin acrylic tub flexes when you step in and you'll feel every bit of that flex for years. Press on the side of any tub before you buy it. If it gives like a plastic cooler lid, walk away.
Small apartment bathrooms do best with a straightforward tub and shower combination, nothing fussy, easy to reseal and keep dry. A family house with more than one bathroom is where a proper soaking tub earns a room of its own, somewhere with a window if you can manage it, because a tub without natural light is just a tub.
A bathtub is infrastructure before it's style, and the ones that look best in ten years are the ones that were built well in year one.