I was W/N for a long time, so I can understand your perspective on making a... permanent class change.
But here's reality, once you step into the pool, you swim around really quick.
Change your secondary when needed. If you're doing general PvE, you can run pure warrior 24/7 and be totally content.
If you're doing specific things, change appropriately. Need Shock for PvP? W/E. Death's Charge for fun in pvE with Cyclone Axe? W/A.
With Tiger Stance now existing, W/R is looking a bit... Lame, unfortunately.
W/Mo... Expect to face a lot of 'Dumb wammo' stereotypes. The W/Mo is the faceless, stereotypcail 'Kill things dont die' class, used by elitists, morons, and everything inbetween. Personally, I try to never use the combination. I personally find it too easy, and only ever go W/Mo for Farming, if absolutely necessary.
Think of what would be fun. Some E skills like Sliver Armor can be mondo fun on a Warrior. Maybe you want to try Teleporting around the area, hacking away at your foes? Whip out a Bow and go /R. Fancy sucking the life from your foes and cursing them (literally)? Hit up /N for good times. Plague Touch is glory if you're going against a lot of conditions. By the same token, Signet of Malice (Assassin) works glory with Sever/Gash. Also, W/A Daggers? Makes me giddy all over, and I'd use it much more often, if people didn't discredit my abilities due to my choice. They work -gloriously-.
I've tried every secondary class for my warrior, and have done a _lot_ in each secondary profession. W/Rt is fun, but only really for the occasional Pain, or a Weapon Skill. As for /Me, the long-lasting stances are very useful, but the energy draining techniques are sometimes less-appealing, though still handy.
Weight the pros and cons for yourself. Decide what YOU want to do in the game. I change my secondary hourly, nowadays. To whatever tickles my fancy, at times. Try them out, and when you find the right one for what you want to do, stick with it... Then try a different one.
I hope this helped somewhat. I'll list some handy skills now, so maybe you can try out each secondary, unlock the skills I mention, run around, and test
W/Mo: Vigorous Spirit, Balthazar's Spirit, Healing Hands (Elite)
W/N: Plague Touch, Unholy Feast, Grenth's Balance (Elite)
W/Me: Physical Resistance, Power Spike, Illusionary Weaponry (Elite)
W/Rt: Vital Weapon, Pain, Consume Soul (Elite)
W/A: Death's Charge, Signet of Malice, Aura of Displacement (Elite)
W/R: Tiger's Fury, Edge of Extinction, Poison Arrow (Elite)
W/E: Shock, Armor of Earth, Glyph of Energy (Elite)
Keep in mind, these are all just suggestions. Try everything out, don't tie yourself down to one secondary.
Good luck, have fun, enjoy the game. Feel free to whisper me or respond here if you need more help.