Terra by Double Helix Glassworks has got to be in my top 3 favorite glass colors to work with. In fact, I would probably say it's my number one favorite, but the people who know me as the "Queen of Raku" would probably tar and feather me. That and the fact that I really do believe that Raku is just a bit more versatile, for me anyway.
Terra and Raku are alike in that they both shift colors when exposed to a high heat in the flame and then allowed to cool before striking, but that's where I think the similarities end.
Raku is a more opaque glass than Terra. The colors can range from earthy browns, to rusty reds, with greens, blues and purples in between. I have found that once struck, it will remain the same color during annealing without any special "lower" annealing schedule. I love Raku for the fact that I can choose to do encased beads or leave them un-encased for even more vivid colors. Either way, I can get the colors to pop and stay that way.
Now with Terra, I find that it's almost translucent when used in thin layers. This can be wonderful for achieving gorgeous boro effects when encased. You can do some really cool wispy encased flowers with it too. But for me, and this is only because my kiln tends to over strike the glass no matter how low I set the temperature, I have not been able to keep the colors through an annealing cycle without encasing the bead. I know this is not the fault of the glass, but rather the kiln that I use, but I still love the glass for all the things I can do with it when encasing it. The color range of Terra is much like Raku except, when encased, it trades the earthy browns for fabulous magenta and golden yellows that I just can't get with Raku.
So I guess when it comes down to it, I would have to say that Raku and Terra tie for first place in my heart.