The overlap in ASA/ISO is because that's definitely not the main distinguishing factor. The most obvious differences are in the color/tone curves and grain characteristics.

There are two color choices in Kodak's "professional" line:

• Portra is, as the name kind of implies, intended for portraits. It features subtle colors and is not very saturated. Personally, I enjoy the look of the coarser-grained Portra 400 over 160; it just seems to have more character. (I haven't tried the 800.)
• Ektar is only offered in ISO 100. It's highly saturated — not what I'm looking for, so, name not withstanding, I generally prefer to just use Portra for non-portraits too. (But, you might find you like the saturated look. It think it's unfortunate that they don't offer anything in between, but I guess the market is rather small these days.

Prior to 2010/2011, Portra came in NC and VC variants, for "Neutral Color" and "Vivid Color". The current version is closer to the previous NC type. (And, has finer grain.)

In the "consumer" line, there's:

• Gold. ISO 200.
• Ultra Max. ISO 400.

I haven't used either of these (except I remember buying rolls of Gold in high school, which is long enough ago to not count), but as I understand it, they have larger grain than the professional film, and Gold is more saturated than Portra but more neutral than Extar.

For black and white, there's also two choices, both also labeled "professional":

• T-Max, in ISO 100 and 400.
• Tri-X, in ISO 320 and 400.

T-Max also used to be made in a P3200 version (intended to be exposed and developed at ISO 3200, although as the P implies, that's pushing its native ISO.)

I haven't used these extensively (that is, I've shot a couple of rolls of each, but never really made a formal comparison, and I've not used the T-Max 400, making any attempt at that kind of irrelevant), but my understanding is that T-Max has higher resolution and finer grain, while Tri-X has more exposure latitude. Except that apparently advances in the Tri-X technology have made it so it has finer grain, too — although people online claim the T-Max still has nicer grain. Shrug — this gets into the highly subjective.

Both black and white films require black and white development and can't be processed at a pharmacy or box store. Kodak used to offer BW400CN, which could be developed using the "C-41 process" used for color film, but discontinued it last year. (So for that, you need Fujifilm Neopan or Ilford XP2.)