Probably a hard call for most to make, for me it is without a doubt the Aerobee Hi. Simple, well executed as a kit, and both reasonable in terms of cost and operation. I get a request to build these every month or so and all it takes is a little effort to produce a creditable model.

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Gravity is a harsh mistress
SAM 002
NAR 91005
"The complexity of living is eminently favored to the simplicity of not."