When the 1977 trinity came out, the PET was the most useful system overall simply due to having Microsoft BASIC. The Apple II had Woz's Integer BASIC and the TRS-80 had an enhanced Tiny BASIC. The following year they all had Microsoft BASIC available.

The PET had the worst keyboard but the most reliable tape system. It could simulate an 80x50 bitmap.

The TRS-80 won on availability, vastly outselling the others due to production and sales outlet capacity. The CPU was about 60% the speed of the others. It could simulate a 128x48 bitmap.

The Apple II had the best graphics (A real 280x192 bitmap mode (monochrome) or 140x192 and colours). Integer BASIC only supported 40x40 graphics. You needed more RAM to support the true bitmap modes. The price was 2 to 3 times higher than the other systems.