BasicAtom

The thing I like the most about it is it's healthy 368 bytes of variable memory. This was crucial to making my GPS rover work.

It also is faster (30,000 basic instructions / second) and has more program space (14k) than the Basic Stamp does.

For $50 you get a lot more capability than a Basic Stamp at about the same price.

I would generally describe my experience with the BasicAtom as positive. After some minor problems getting the development environment setup - things generally worked as documented.

The documentation itself has recently been revamped and now looks to be of high quality.

Note: The "BasicAtom Pro" is an entirely different animal. It's the same concept, but is based on a different chipset. It is more powerful, but I've found it to be significantly more problematic to work with than the non-pro version of the chip.

Although not as popular as the Basic Stamp, the BasicAtom has a large following. Lot's of sample source code for interfacing with various devices is readily available.