Is there really such a thing as “hardest genre”?
Yes. But not in the same sense as you might think. If you let Segovia learn and play Rock, he might not be as successful as with classical music. If you let Jimi Hendrix play the Jazz, he might not be as successful as with Rock music. If you let B.B King play Bluegrass music, he might not perform as well as with Blues music.
Bottom line is, each individual have his own style, his own perception of music, and so will overall perform better in one genre than another.
However, if we are to take each genre individually, and try to analyze it in terms of technical difficulty, theory and philosophy, then I'd have to say (and I know many experts will agree with me) that, the Jazz is the most difficult one. Maybe only the Flamenco will beat it, but only on the classical guitar.
Should I be playing it? or otherwise what genre to choose?
Short answer is this: No, you should instead pick a genre that you enjoy playing and listening to. Because at its core, the only reason for you to play and make music is entertainment, and your enjoyment and self expression. Music is not a university subject (I know there is Music major in universities, but those are for theoretical and historical study ONLY. No body will ever ask you to hold a random instrument and force you to play it, especially not in a university. REMEMBER THAT).
So really, just learn and play the music that you truly love, regardless of the difficulty or the history of the genre, because good amazing music come only from the heart. You can be the most technical guitarist in the world and can shred the guitar like no one did before, but if you hate it (was forced to play by your parents, for example), you won't be able to play with passion, your performance will be very generic, you won't be creative or productive with the guitar, and eventually you'll put it down and stop playing forever.
So be wise and, follow your heart!
While we're at it, allow me to make a quick and short overview of three of the most popular genres out there …
Jazz, originally created by the African-american communities in the late 19th century, is, according to many guitar expert players (that I personally had the privilege to discuss this with), probably the most sophisticated music genre out there. Improvisation is one of its key elements, which already requires a person to have some advanced background on music and good understanding of the scales (refer to my other post about Improvisation). It is a very beautiful, yet difficult, music genre. If you have a background on the Jazz and you enjoy listening to Jazz music, and want to learn it, I first congratulate you on the excellent choice and taste in music, but be prepared to work hard and dedicate a lot of time and effort into practice and training.
Artists for reference in this genre are: Billy Holiday (singer), Django Reinhardt (guitarist).
Is another popular and classical genre that originated first in the African-american society in the United States, allegedly at the end of the 19th century. it is identical to rock music (or more correct to say – rock music is identical to blues, as rock music was born from the blues and was highly influenced by it especially in the early years of its creation) in many aspects, and many artists out there are famous for being both Blues and Rock stars altogether and perform in both Rock and Blues gigs, such as Stevie Ray and Eric Clapton.
Difficulty level: I would say more difficult than Rock, less difficult than Jazz. (Of course, generally speaking)
Famous artists in this category are: B.B King, Ma Rainey
Rock music is a very popular genre if not the most popular one among them all, originated mainly in the United States in the mid 1900's under the famous name “rock n roll”, and was widely used and practiced both in the U.S and in the United Kingdom. It is considered relatively easy to play and a good choice for beginners to introduce themselves to the guitar and music theory in general. Although it's relative easiness among the other genres, rock music have branched since its establishment into many styles and sub-genres, like the heavy metal music, funk, country-rock and blues-rock, just to name a few, and it's simplistic, yet amazingly beautiful and soulful nature, which can make you jump off your chair and fill you with exciting live energy, or in the opposite warm your heart and soul, have made it easy to touch the hearts of countless fans around the world past and present, me included. I'm a huge rock fan!
Honorable mentions in this category would be: Jimmie Hendrix, Led Zeppelin, Elvis Presley, Queen, Pink Floyd, Rolling Stones, and so many more.
You should be playing the genre and the music that you have passion for, and feel connected to the most, regardless of difficulty or any other factor that might be involved. Music comes from the heart only, and it will come from your heart only if you enjoy it, and want to play it.
While the Jazz wins the crown for the most difficult genre from the point of view of many artists and guitarists, me included, I'll take the opportunity here to add one more thing:
ALL genres at some point on the highest difficulty level, will become more or less equal in difficulty, because while the scales might still be the same for each genre, the techniques and the complexity of the licks and solos at this high level will be almost the same.
Even for a relatively easy scale such as the Pentatonic scale, you can create extremely hard licks with string skipping and tapping that can challenge even the most renowned guitar players in the world.
Just check the likes of Paul Gilbert and John Petrucci and what they are capable to do with the guitar, in the genre of Rock and Metal.
While we're at it, a quick reminder: No body has succeeded yet in sounding like Jimi Hendrix, who himself is a rock legend and ranked as number one guitarist of all time in the Rolling Stone magazine.