Firmware 1.5
+All 1.x Homebrew runs with no compatibility issues
+All 2.x Homebrew runs with no compatibility issues (via DevHook)
+More support for customization tools
+Almost all ISOs run (via DevHook)
+Customize emulated 2.71 emulated firmware without the risk of bricking your PSP
+Directly Boot any homebrew
+Recovery Menu to prevent Soft-Bricks (Custom Firmware)
+Skip autoboot UMD (Custom Firmware)(Also skips boot splash screen)
+Hide Corrupt Icons (Custom Firmware)
+Run non-kxploited Homebrew (Custom Firmware)
+Load PRXs from the Memory Stick at boot (Custom Firmware)
+Doesn't VOID your Sony warranty if you DO NOT install the Custom Firmware (Unless they can PROVE your ran homebrew, then they would void your warranty)
-Does VOID your Sony warrantly (only applys to current psp systems since they will know its firmware version by the serial number, not to US/JPN Launch systems)
-Memory Stick Corruption issues with emulated firmwares
-Speed decrease by emulating firmware from memory stick
-Requires UMD for emulation (via DevHook)
-Must browse ISOs with shortcut keys one at a time via emulated XMB
-Must restart DevHook to run a UMD via DevHook 2.71 Emulation
Firmware 2.71 SE-B'' (B3)
+Runs almost all 1.x Hombrew (does not need to be kxploited to run)
+Runs all 2.x (PRX) Homebrew
+Run UMD or ISO without having to restart
+Runs newer UMD games directly (SE'' if it does not require 2.8x kernal features)
+Run games with plainprx files (SE'' this is working correctly)
+All Games load in Devhook when using 271F if systemctrl_dh4se.prx is not loaded (not sure with the SE'' version if it has fixed these issues)
+Runs almost all ISOs (DevHook via MemStick emulation has better compatibility)
+Some ISOs that do not work in DevHook properly now work (Ex. bost-a-move)
+Runs a large number of ISOs with no UMD
+Skip autoboot UMD (Also skips boot splash screen)
+Hide Corrupt Icons
+Run non-kxploited Homebrew
+Firmware performs faster (Browser, RSS, Games)(Because it's stored on FLASH0)
+No known memory stick corruption issues
+Browse ISOs via the Game Menu in the XMB
+Recovery Menu to avoid Soft-Bricks
-Compatibility Issues with SOME 1.5 Homebrew
-Not all ISOs work with built in Emulation
-Not all ISOs work with DevHook if DevHook is using FLASH0 for emulation of 2.71
-Some have issues with it not functioning properly (CAN be fixed by flashing a working 2.71 FLASH1 used with DevHook previously)
-Uses up more space on FLASH0 (Altho this should not be an issue, as it is not full)
-If you change your boot screen then run an update it MAY Soft-Brick your PSP (this is because of the limited room in FLASH0)
-Must flash FLASH0 to customize, not as many tools to support this
-VOIDs your Sony warranty if it bricks
Sources:
http://forums.maxconsole.net/showthread.php?t=34532