bill, I own a proxxon mf70 (check model expo) and have used a sherline.
I have heard that the harbor freight machines are sturdy but not so accurate. hearsay only. heard of taig but cannot recall anything that stood out.
from experience I think a sherline is ok but requires some careful use and setup.
the proxxon is very small (they do offer some larger models) but I have been pleased with the accuracy out of the box and also the ease of adjustment. bang for the Buck Has been quite good.
one concern is that to use very small mills you need a very high rpm, which most mills cannot do. the proxxon does. and for the tasks you describe a 3/8 that bit will work, sure, but is overkill. think of milling off molded on grabs...
so my 0.02 is to take a look at the proxxon, but the sherline should serve.