How many 8088 PC machines are there? Well, here is a list of the important ones:

IBM PC
Pros: This is the original PC, from which all future devices come from. This is the ultimate in compatible devices, upgradeable video, math coprocessor available, cassette support (only it and PCjr. have fully functional cassette basic), only three realistically available slots.
Cons: No native support for 720KB drives, only 256KB on motherboard, XT has more slots, everything except the keyboard and cassette recorder requires an ISA card, serial support limited to 8250 UART chip, first boards support only 64KB on motherboard and don't scan for card ROMs, weak power supply, will not fit PGA adapter, no hard disk standard, early drives single sided, no 101 Keyboard support.

IBM PC/XT
Pros: Slightly more advanced than its forebear, some can support 101 Key Keyboards and 720KB drives, eight ISA slots, more powerful power supply, often come with hard drives and async adapters, can support 640KB on motherboard natively or with painless hack, upgradeable video, can support four floppy disks.
Cons: No real improvement to the PC, support limited to 8250 UART chip, two slots only support short cards, need DOS to saving/loading BASIC programs.

IBM PC Portable
Pros: Uses XT motherboard, all advantages apply. Comes with CGA adapter.
Cons: It weighs 31 Pounds! Cramped system case means only two long cards and up to two half-height drives only. Amber monochrome composite monitor (TTL is better.)

IBM PC Convertible
Pros: It runs on a battery or AC, native support for 720KB drives, two 720KB drives included, emulates MDA, true CGA, faster SRAM, supports internal modem, user replaceable fonts, composite video support w/CRT adapter, backlit LCD available, upgradeable to 640KB.
Cons: First screen not suffers from low contrast, 2-color LCD display, extremely limited expansion options, fully expanded weighs almost 20 pounds, no hard drive allowed, no math coprocessor, no support for TTL monochrome monitors, tweeter instead of speaker, no sound cards available, one serial & parallel support only, no joystick support.

IBM PCjr.
Pros: It runs cartridges and PCjr. specific software, wireless keyboard, better graphics modes, built-in serial & modem support, supports many games with Tandy graphics, two joystick ports, cassette port, composite video support.
Cons: Limited expansion options, one floppy drive, no hard drive, no math coprocessor, some incompatibility with CGA & Tandy graphics, slow memory performance, extremely weak power supply, flaky wireless, terrible chicklet keyboard, fewer keys, proprietary connectors, sidecars increase computer size, lack of IBM support, no video or audio upgradeability, no 720KB drive support, no DMA, no on-board parallel, only one serial port, non-IBM options somewhat difficult to find.

IBM PS/2 Model 25
Pros: See Model 30 for list.
Cons: In addition to Model 30's, Integrated Monitor (could be burnt-in, monochrome, small), 2 ISA slots.

IBM PS/2 Model 30
Pros: 8MHz 8086 processor for better performance, supports PS/2 keyboard + mouse, full support for 101-key keyboards, support for 16550 UART serial chip, one parallel, two serial ports built-in, MCGA onboard, upgradeable video, 20MB hard drive available, math coprocessor upgradeable.
Cons: Three 8-bit expansion slots, no 4.77MHz speed, tweeter instead of speaker, no composite video support.