Many of these shows are available on Youtube, and those that aren't probably aren't worth watching.
Marvel's first entry into the live-action genre was Spider-man's appearance on The Electric Company, way back in 1974. After this Spider-man got his own TV show, The Amazing Spider-Man, which lasted until 1979. Near the end of The Amazing Spider-Man's run The Incredible Hulk TV show appeared, which was undoubtedly Marvel's most successful show up until that point. A few other shows followed - none of any real consequence - up until the Spike network aired the Blade TV series in 2006.
By comparison, DC has had a much more successful run of TV shows. The first DC character to appear in his own show was (of course) Superman, way back in 1952. The 1960s Batman television show is one of the most recognizable TV shows of all time, and later shows such as Wonder Woman in the 1970s, the original Flash in the 1990s, Lois & Clark in the 1990s, and the well known Smallville in the 2000s were all quite popular.
Recent or Ongoing Shows
Most of the shows listed below tie into Marvel's cinematic universe, while the DC shows seem to occupy a world all their own.
Agents of S.H.I.E.L.D
Agent Coulson and crew attempt to deal with super-powered threats using an array of sophisticated weaponry. B and C-list characters such as the Absorbing Man appear in this show, and recent plot elements have hinted at the Inhumans.
The plucky Agent Carter and her companions do battle with H.Y.D.R.A. This series is set in the 1950s, and ties into the backstory established in Captain America: The First Avenger. I've heard rumors that this show will be canceled.
A Marvel property in name only, with only an Icon imprint title to boast of. Detectives track down rogue superheroes. The guy from District 9 stars, along with a bunch of people you've never heard of.
After losing his sight in an accident, Matt Murdock develops heightened senses that allow him to "see" things that others don't. After beginning a career as a vigilante, he faces off against the Kingpin, the crime boss of Hell's Kitchen.
I've only seen a few episodes of this show, but as anyone can tell you the Green Arrow is basically Batman with a bow and arrow. This show was very "cutting edge" for a while, but in the wake of shows like Daredevil it seems behind the times.
A show about Batman before he was Batman. I've seen previews for this show, but nothing about either the previews or later reviews has made me want to see Gotham. What's the point of a show about Batman that's missing Batman?
After an accident involving a particle accelerator, Barry Allen develops the ability to move at superhuman speed. I've seen every episode of this show so far, and I'd have to say that the episodes have varied in quality quite a bit.
I loved the movie based on this character, but I have yet to see the TV show. It's been getting terrible reviews, and I just can't be bothered with it. A guy who talks to the dead does battle with the forces of evil.
Never seen this one either. Zombies? At best, only tangentially related to the world of DC comics.
The Best of the Best, or the Best of the Rest
As far as current Marvel shows go, Daredevil is the hands-down winner. This show works on so many levels that it's ridiculous. The performances exceed anything seen in any superhero show ever, and the writing is top notch. Aside from his disappointing face mask and an ending that felt somewhat rushed, this show is nearly flawless.
Agents of S.H.I.E.L.D. and Peggy Carter, by contrast, offer boring characters caught in formulaic situations. Neither of these shows have actors that could really carry their own shows, and I think that if they didn't have "Marvel" above their names they would have never happened in the first place.
I haven't seen enough of Powers to judge it as harshly, though what I've seen was underwhelming.
The Flash is definitely the best of DC's shows right now, with Arrow a distant second. Tom Cavanagh, the guy who plays the Reverse-Flash, really makes the show, and even though the "CW-ness" of the show is a mark against it, the romantic subplots can be ignored once the action gets going.
As for the rest of DC's TV universe, I'd like to reiterate the fact that Daredevil is an excellent show that can be watched more than once, and there are more episodes of The Flash on the way!
Marvel has a whole series of Netflix shows planned, the next being A.K.A. Jessica Jones, which features an ex-superhero investigating current superheroes accused of wrongdoing. Hey, isn't that the premise behind the Powers TV show? Maybe, but I'm sure it'll be better on Netflix.
After that we'll see shows featuring both Luke Cage and Iron Fist, leading up to another show featuring the Defenders. There has been talk of these Defenders making a cinematic appearance in Avengers: Infinity War Part 2, and that's something that has me excited.
DC is now filming the Supergirl TV show, which does not interest me in the least. There is also an Arrow spin-off featuring the Atom in the works, as well as shows featuring Lucifer, Preacher, and the Teen Titans. I'd probably give the Teen Titans show a try, but the rest will probably pass me by.