Normal vs. hard tension is a bit of a dilemma for new to nylon players I think. I've tried both and will stick with hard tension. Coming from the steel world, here are my thoughts so far (with visual aids for fun).
Normal Tension:
Easier to barre
Nice on fingers
Easier to play out of tune due to too much pressure or side bending
strings feel and sound more floppy when playing harder, go sharp easier
Hard Tension:
Still easy to barre
Still nice on fingers
Makes playing in tune easier
Can play harder without things sounding floppy and going sharp
It all depends where you've come from. If you have been playing steel string for years I'd go hard tension, unless the guitar builder says you can't. Consider the following numbers:
Daddario EJ16 "12 gauge" steel set has a total tension of 160.51 in/lb
Daddario EJ17 "13 gauge" steel set has a total tension of 185.27 in/lb
Daddario Pro-Arte EJ45 "Normal Tension" has a total tension of 85.85 in/lb
Daddario Pro-Arte EJ46 "Hard Tension" has a total tension of 89.94 in/lb
If you are used to 12 gauge, you are dropping almost half the pressure. If you are used to 13 gauge, you are dropping MORE than half the pressure. I always played with 13 gauge or bluegrass gauge (12's on top, 13's on bottom). As such, normal tension felt quite rubbery at first. I was trying to adjust, then tried a guitar with Hard tension. I instantly sounded better and cleaner as a player. Hard tension will also allow you to get your action a hair lower. That means less strain on the wrist and improved play-ability.
One trade off would be the ability to bend notes into pitch by just pressing harder when they fret flat. That will get harder with hard tension. Although I have found it easier to control with harder tension. And thank you Todd for that bending tip!
Todd... Tip. Todd Tippton... too funny. As a side; Dr. Tippton, you are the doctor of tips! Seriously though, I am enjoying your comments on this forum and am learning from them! Thanks for all your posts.
NOTE: I am new to nylon string. I've played guitar for almost 30 years, but only a month or so on nylon. I certainly stand to be corrected.