My first technically was a TRS-80 Model 1 Level 1. But We couldn't afford to buy one, I used the one in the local Radio Shack. My first computer that I actually owned was one that used the RCA CDP1802 CPU. They were a LOT of fun to program - simple 91 opcode instruction set and VERY logically organized. And amazingly flexible - 16x16 bit registers, and any one of them could be the program counter, switchable on the fly, any could be the index register, switchable on the fly, etc.