Yep, the competition between DC and Marvel means that the fans are the winners
Hopefully, gone are the days of crap comic book movies being made
Really the only competition between the two studios is with the fanboys. WB/DC and Marvel would have what I imagine to be a friendly rivalry I reckon. Marvel wouldn't be hoping for DC films to fail, or vice-versa. One good comic book film makes people want to go and see another...and then another.
They will try to one-up each other in terms of announcements at times (like recently) and will smile when they have a bigger box office...but there is no hatred between the two companies.
You are right though, it is the fans who are the big winners from all this.
Although the days of crap comic book movies will always be around - there will just be a lower percentage of them than there was previously.