When they first brought in the certifications for sub classes I gave the chance barrier a try and I didn't like it for my main. It was just 1 more thing to wait on to work my hp for skills. My choices were pretty straight forward:
Chance Haste
Passive Crit (note, this adds to BASE crit rate....before you equip a weapon)
Everything else I threw at strengthening the weak point of titans; mdef.
Here's some info that might help with your decision:
http://vnmedia.ign.com/l2vault.ign.com/images/CoolFind/subclass%20skill%20tree.jpg
Warrior (Destro, BH, Tyrant, Glad, Warlord, SB, BZ)
Passive Greater CP Boost: +738 cp
Passive Resist Debuff
Active Chance Haste: +32% atk spped, 15 sec, 5% trigger rate
Rogue (Dagger/Archer, Arb)
Passive Long Shot: +100 bow range
Passive Boost Evasion: +4 evasion
Active Chance Critical: +30 crit rate
Knight (Pally, DA, TK, SK)
Passive Greater HP Boost: +6%
Passive Resist Critical Damage: +3% reduction
Active Counter Boost Mdef/Pdef: +20%m/pdef, 15 sec
Summoner (Warkock, PS, ES)
Passive Boost HP/MP:
Passive Resist Elements: +5 resist
Active Boost Cast Speed/ Power: +7% matk, +8% cast speed, 15 sec
Nuker (SH, SpS, Sorc, Necro)
Passive Boost Mdef: +20 mdef
Passive Boost Recharge Rate: +20 mp per recharge
Active Counter Mana Vampire: 10 mp, 3% chance (17mp w/mana gain passive)
Healer (SE, EE, Bish)
Passive Increase Self Healing: +19 HP on heals
Passive Resist Divine Elements: +5 resist
Active Counter Self Heal: +183 HP, 3% chance
Enchanter (PP, WC, BD, SwS, Inspector)
Passive Greater MP Boost:
Passive Boost MP Regeneration: +0.5 MP/tick
Active Counter Invunerability: 5 sec, 3% chance
The ones that are blank I never really found the info for yet. Might sooner or later