Just to keep the record straight, the justifyably popular Green Zebra is not an heirloom. It was bred by Tom Wagner, one of several of his modern OP tomatoes that are erroneously grouped with heirlooms.
Which raises an issue little addresed by folks who have jumped on the heirlooms bandwagon: Not all open pollinated varieties are heirlooms. But that doesn't mean there aren't some great modern OPs. The reasons for breeding modern OPs are not the same as the reasons for breeding hybrids.
Black Krim is also popular, thanks, in part, to Martha Stewart touting it. Personally, I'm not as enthused as other people. Indeed, I'm on record as calling it the most over-rated tomato in history. Be that as it may, there are better blacks than that one. Paul Robeson, for instance. Southern Nights, also from the Crimea, is the best black I've ever tasted. But there are two problems with it for the home grower. It's indeterminate. And seed is not readily available.
I'd have to agree about Riesentraube. One of the few cherry tomatoes I can eat; most of them are too sweet for my taste. If I want a candy bar I'll munch on a Snickers. But the Riesentraube has a complex flavor that tastes like a tomato. Black Cherry also is a good choice.
I wish you could remember which white you found tasty. In my experience, and that of most folks I know, the whites do bring that color shift to the table. But not much in flavor. William Woys Weaver has been working on a major exploration of white tomatoes, and keeps threatening to write an article about them. But he has so many draws on his time it keeps sitting on the back burner.
If I were forced to choose just one tomato to grow it would be Cherokee Purple hands down. It is, of course, as ugly as homemade sin. But the flavor more than makes up for its lack of physical charm. And it will, apparently, grow anywhere in North America that tomatoes can be grown.
Fortunately, I don't have to make that choice.