I'm not sure aside from the IIc+ there is a specifically desirable IIc. The real early ones had serial port limitations, and you can upgrade the system ROM
versions in them if you're so incline. But generally a IIc seems to be
a IIc and thats about it.

Yeah, that odd sized serial port (compared to everything I own for Mac/Apple that would otherwise be compatible) is a pain. I've never got round to
making an adapter so that machine doesn't get much use. But it works well otherwise and in terms of storage space for collecting it is is quite small.
I preferred my IIe Platinum but one had to go. Small space won out.

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