I don't know much about ECW but I do know a bit about WCW.
WCW was started from scratch by Ted Turner (a media billionaire) in Seppoland. They threw money around like never before and lured some of the biggest names from WWF to WCW. These names included Bret Hart (which led to the infamous "Screw Job"), Hulk Hogan, Kevin Nash, and Scott Hall.
WCW really killed themself off by some really bad writing and gimmicks. They continuously relied on 3 or 4 big names and hardly ever pushed anyone else up. It really annoyed some of their younger talent (Chris Jericho is one that springs to mind) and they jumped ship over to WWF when their contracts were up.
Whenever a wrestler had an idea, the company would listen to it, say no then push one of the big 4 again. It just got stale.
In the end, WCW was bought by WWE for an embarrasing amount. Vince McMahon also got control over the WCW belts and their library of tapes.
Some of the worst ideas by WCW included
1. Lining up over 100 wrestlers for Goldberg to run through in about 2 mintes flat.
2. The tag champions of WCW ended up being one wrestler (I can't remember) and Buff Bagwells MOTHER. Geez.