At the moment I'm usign IDA 4.3 and have only downloaded IDA 4.51 to read help file to discover what's new... I can tell You more in the next week when I'll install and work with it...
After reading new features I can tell You that's still the best DISASSEMBLER and a MUST HAVE TOOL if You're interested in reverse-engineering. To mention the reasons You're talking about i could fill up few screens full of text. Just download this prog and start to explore... You won't be disappointed... The PE-Debugger is very deep and efficient but only in specific cases. You should first try SoftIce, TRW, OllyDbg or Debuggy as your main debugger and then, if You're still And about SoftIce and OllyDbg - I'm using all these tools together and don't know why You would have to choose (only) one.

Greetings!