As an extremely happy owner of Komplete 3, anyone who is just getting started in the world of MIDI synths and samples shouldn’t even think about. Just buy it! Komplete 5 for $400 is a stupidly cheap price. I thought that Kontakt 3 (included) alone would cost that.
Komplete 3, while using older versions of most of the included synths/samples and missing Massive and Akoustik Piano, handles about 85% of my MIDI sound needs. In fact, the only time I reach for anything else is when I need real drum sounds and sometimes real bass sounds. (I use Superior Drummer 2.0 and East West Hardcore Bass generally for those.) With that said, I do reach for the Stingray samples quite a bit in Kompakt.
I remember when they cut the price in half on Komplete 3 several years ago and they were charging $600 for it. I thought this was an insane value (and it was!). To jump into the world of MIDI sequencing for only $400 should be illegal. If you are considering going the MIDI route, I can’t recommend Komplete 5 any higher. You will be happy!