I'd have to say the Quadra 950. With it's Motorola 68040 processor running at 33 MHz, maximum RAM of 256 MB, maximum onboard VRAM of 2 MB, 5 Nubus slots, 1 processor direct slot, two SCSI buses, built-in ethernet and room for up to 4 internal drives it didn't have an equal in the desktop market. In fact the systems that matched it's performance at the time were workstation class systems from Silicon Graphics (like the IRIS Indigo*), Sun Microsystems and NeXT Computer.
And when outfitted with A/UX 3.0, it was able to compete in the workstation market.
At the time (1992) this system was outside the range of most Mac users. The based Quadra 950 started at around $8,800, and maxing out the RAM would have doubled that price. Adding A/UX to the system would have added another $1,200.
*At this point in time Silicon Graphics was making a push into the desktop publishing market with their MOM (Move Over Mac) initiative. The IRIS Indigo was about the same speed as the Quadra 950 and priced about the same (about $10,000 for the base system). What it didn't have was the expandability. It had a maximum of 96 MB of RAM, two expansion slots, a replaceable graphics board (optional 24 bit graphics or 24 bit graphics with 4 geometry engines) and room for three drives.