Hi Tom: A table saw is a must prior to compound miter box or any other floor or bench mounted power tool, IMO.
If garage style portablility is a priority, I'd consider a portable contractor's 10" saw like the Makita, Delta or DeWalt. To keep them light and portable, these usually have either cast aluminum or stampled tables, and are often direct drive. I can think of no 12" portable table saw. I'd steer clear of the B&D, Craftsman or Skil portables with their much lower sales prices.