I'm interested in starting up a sports manga

Which one should I read though?

I've heard great things about Hajime no Ippo, Slam Dunk and Eyeshield 21.

Eyeshield 21

It's already finished, goes for about 300 chapters and Hiruma is about one of the most hilarious characters ever.

Well, When it was on Toonami, I watched a bit of Prince of Tennis. Thought it was kinda neat.

Hajime no Ippo is alright.

Slam Dunk seemed fairly entertaining. Read some chapters in the American Shonen Jump, and it was far from bad.

Air Gear if you would consider that a sports manga.

Slam Dunk is great, am about a third through, and so far I like it a lot.

You should read Air Gear nomatter what.

And Slam Dunk it's hype is through the freaking roof.

eyeshield 21, hajime no ippo, and air gear are all nice choices, and i'd suggest teppu (for professional mixed martial arts), over drive (professional bicycling), kuroko no basket (basketball), and bamboo blade (kendo) as well.

though onemanga has suspended air gear and bamboo blade due to adult content (though i havent seen much of that in the latter, but whatev.) so you'll have to read them elsewhere if you dont already.