There are a number of options out there!
Firstly are you planning on using a PC or a Mac as some software is only available for one or the other platform- MOTU Digital Perfoermer is MAC only whilst Cakewalk Sonar is PC only. Emagic Logic will soon become Mac only (although who knows if there will be a mass outcry from disgruntled PC Emagic users???????). Steinberg Cubase and Nuendo are for both platforms.
All of the above mentioned programs plus others are very powerufl in their own rights and get the job of music production done very well indeed!
I personally use a Mac G4 running a Digidesign Digi 001 system with Protools LE- this is great for audio but weaker for MIDI. I also have Logic Audio GOld which is the best for Midi but I find it more cumbersome for audio although other would not agree!
It all comes down to what computer you are using and what software you are comfortable using! If running MAC give Motu Digital Performer a good going over! I am gonna check out this program soon. The new Cubase SX and SL look very interesting also although personally I find the interface too colourful for my taste!
Logic is great and the plug ins a numerous and of high quality.
Basically there are alot of options out there! Good luck

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