Between the PC (3), XT/ Portable (3), PCjr.(1), AT (3), Convertible (1) and XT 286 (1) there are ten BIOSes. I would prefer an emulator that emulated each systematically rather than the aptly named MESS. I would want an emulator that would allow you to configure the Floppy Disks, Hard Disks, RAM, Graphics and Sound Cards, co-processors, serial and parallel ports with real accuracy, including limitations:
IBM PC - Five full-length 8-bit ISA slots, a cassette interface and a maximum of 256KB on the motherboard. Two full height 5.25" bays. 83 Key Keyboard and 360KB Floppy Drives. First two BIOSes use a 16-64KB boards, third BIOS uses 64-256KB board. 8 Interrupts/4 DMA channels. Keyboard + cassette connector only.
IBM PC XT - Eight 8-bit ISA slots, 6 full-length, six full-length. First BIOS comes with 128-256KB, 10MB Hard Disk. Two full height 5.25" bays. 8 Interrupts/4 DMA channels. 101 Enhanced Keyboard, 720KB Floppy Drive, 20MB Hard Drive and 640KB on motherboard support with the Second BIOS. Keyboard connector only.
IBM PCjr. - 64 or 128KB. Enhanced CGA only. Internal Modem not Hayes Compatible. 8 Interupts/No DMA controller. Two 64KB cartridge slots. 62 Key Keyboard only. One 360KB Drive. Buzzer, not Speaker. Ports for Light Pen, two joysticks, serial, cassette, composite video, audio, one sidecar port.
IBM Portable PC - All comments I made above for the XT, First BIOS apply, except this came with a CGA, which connected to a 9" amber monochrome composite monitor.
IBM PC AT - Six 16-bit ISA slots, two 8-bit ISA slots, all full-length. Two full height 5.25" bays. First BIOS supports 14 types of Hard Disk. 128-256KB. 1.2 MB and 360KB Floppy Drives supported. 20 MB Hard Disk. Second BIOS throttles CPU speed to 6MHz, supports 720KB Floppy Drive, 512KB, 22 types of Hard Disk. 30MB Hard Disk. Third BIOS throttles CPU speed to 8MHz, supports 1.44 MB Floppy Disk and 101 Enhanced Keyboard. 16 Interrupts/8 DMAs. Real time Clock.
IBM PC Convertible - 80C88 processor, static RAM, 256KB, upgradeable to 512KB. CGA adapter built-in. 640x200 monochrome LCD displaym but can connect to a composite/RGB monitor. Internal modem, parallel/serial adapter available. 78-Key Keyboard. Two 720KB drives.
IBM PC XT 286 - Five 16-bit ISA slots, three 8-bit ISA slots, six full-length. 640KB on Motherboard. Supports 1.44 MB Floppy Disk and 101 Enhanced Keyboard. 16 Interrupts/8 DMAs. Comes with 20MB Hard Disk. 6MHz 286 with 0 wait states (All ATs have 1 wait state.) 24 Hard Disk types support. Real Time clock.