I love this, instead of complaining you come hear to ask for help. Huge respect!

Nearly every gank is over in the first 3 seconds, we either kill you or we run. So what you are going to want is something that can help you survive that first 3 seconds and then recover to full so the ganker must retreat.

Multiple sets can help you achieve this, but I personally like zoal's. Actually never once got ganked while wearing it and it has thwarted many of my own gank attempts. Only a 2 piece set as well! Its almost perfect, but it has two weaknesses.

1: ranged gankers can still attack without getting feared
2: Immovable potions can allow attackers to ignore the fear

Luckily ranged gankers are bottom of the barrel in terms of damage and skill, so as long as you keep your passive defenses tight they will be nothing more then a mild inconvenience. Keep major/minor protection up and have at least one defensive champion point such as ironclad. A plentiful amount of crit resist is also helpful to avoid an insta kill from a ranged attacker.
Their only trick is to try and use the bow ultimate on you, which is easily countered by a tree or rock. Yep just roll until you reach cover and they will have nothing left to try to kill you.
Immovable potions are pretty rare for gankers to be using and they would have to already know you are wearing Zoals. Its fine though everything should have counters and thats why you don't completely rely on tricks like Zoals.

After you survive a gank you are going to be in huge pain, hp probably in the execute range. Your first instinct will probably be to roll, but do not do this! Almost every ganker is using the dual wield execute to finish off targets and it cannot be dodged. Instead you should slot your class insta heal and block cast back to full hp before trying to fight back. Block casting is like ganker kryptonite, we cant handle it. Its the reason we have to kill anyone good in the first 3 seconds.

As far as other defensive sets goes I think thats up to you, but I wouldn't advise relying on high armor! Nbs have tons of armor penetration and we laugh at anything less then a full on tanks armor. Try using sets that offer non armor based damage mitigation, but only use one. You don't need zoal's and two defensive sets to fight gankers. Have over 30k hp at a minimum to insure they do not burst you down with the sneak attack.

Right now dk, warden, and templar are the big nuisance classes to gank. Either of these 3 have amazing heals for the block casting I mentioned earlier. Block casting it literally just holding block while casting a skill, its easy. So slot a BIG heal, a stealth detection ability like flare(also gives major protection), zoals, one defensive CP, and one defensive set that isn't an armor buff. Rallying cry is a good set for defense and offense. If you keep that buff up you will have a good crit resistance buff and damage.

Good luck though, because even with all of this they can simply outplay you and win anyways. You will have the advantage however and I know with this you can at least survive the sneak attack/follow up execute. In the event that they do not give up after you survive the burst try to keep pressure on them with detect potions, a gap closer, and strong burst aoe abilities. If that can't cloak they will probably try rolling, so you are going to want undodge able attacks to keep the pressure on them. If they can't roll away they will try running, so that is why you pop the detect potion and use gap closers. You can easily win a prolonged fight against a ganker, they simply are not built for it.

Sea serpents coil is 40 percent damage reduction
Run over 35k hp and most nb won't bother attacking you
There are sets like Phoenix and berserker that give you a big heal if you are low hp

Thank you very much for all the answers. I play mostly healers and tanks, so HP will not be an issue XD
Ok than, Zoal is a must, as well as slippery. The rest I can figure out.

Thanks again and cheers!

Harbingers and high damage mitigation combined with lowest block cost you can get

Zoals Zoals Zoals