You'll be perfectly fine, the mage and druid alone could duo nearly anything up until PoP. At that point you may run into some issues without a slower / haste / mind candy however.
Druid / Mage / Necro seems like I would be a decent combo. Can't say for sure though, I'm not much of a boxer really.
Warrior is a terrible tank to box. Requires way more attention to hold aggro than a knight and offers far less utility. Also, where are your slows? Not sure why you would bother to box a tank without a slower, especially with a druid healer. Change the warrior to an SK and the mage to a BST and you might have something halfway decent while maintaining the play style you seem to be going for.
Mage/Mage/Mage is hilariously broken until the era when AEs can't be line of sighted, named rampage etc.
If I were making a 3 box I would go with: Mage, Necro, Chanter or Druid Pets are pretty self sufficient for the first couple expansions and Chanter would bring slows, mez, stun, and crack where druids would bring ports, dmg, heals, and buffs. depends on if you want Slows/Mez or Ports and Heals really imo. Mages are also awesome for groups because you can get any of your characters in a group and use the mage/necro outside the group for "extra" dmg. I can't tell you how many camps I was able to get into cause I had pocket mages that would dps outside the group as well. Go with enchanter and you can find groups easy with the enchanter and then use mage/necro as the selling point of why you should get into that group over someone else
I've boxed War without aggro issues. Equipment and AAs matter a lot. I agree that an SK would offer a lot of utility early-on, but one reaches a point where they need a War to tank content.
I boxed mage, enchanter and druid, and only ran into problems tanking named mobs 5 or 6 expacs in. Then I added a SK, and was very happy with the 4 box combo. Without the SK, the only thing you lack is a true tank and FD. (And rez at early levels. They F'ed up last progression and I got a rez on the druid like 5 expacs early). Mage and druid are super easy to box. The only real negative is two cloth classes. Life is a lot easier if each box has their own type of armor. This time around, I am planning on Monk, Druid(or shaman, I prefer ports and snare to buffs) and enchanter. I might go SK, druid, Enchanter, but DPS will be an issue.
C'mon do ones that will be fun, not just efficient! Pally/Necro/Beastlord Rogue/Monk/Shaman SK/Druid/Mage I dunno, there's probably lots more fun ones.
pally / mage / dru this will be my third progression paladin. are they terrible? kinda. but simple to gear because like five people roll them and everyone loves flaming swords!! sooo much rotting CLR/PAL nodrop gear, even in classic. being the only half-elf female paladin on the entire server is fun. nobody looks like you!
Hmm I was considering monk/shaman (classic 2box) but was pondering if the server get up to the expansions with missions to add a 3rd char so I can request missions myself if needed... I got pull, slow and heal but what if I add a druid for the healing and use the shaman for slow/dots and the druid also adds mana regen during luclin, also ports, ds and decent heals, definetly enough to keep the monk alive with slowed mobs. up until like the most current expansions. Monk would be main IF I find a decent euro "raid" guild.
I think if I did a 3 box crew, it would be this: Enchanter/Druid/Mage Enchanter for charm dps, mind candy, slow, cc, fear, other buffs, other debuffs. Druid for snare, heals, charm, evac, dps, buffs, debuffs. Mage for pet, dps, pet toys, debuffs, buffs, charm. Enchanter/Druid is the main combo as a charm team (snare being one of the defining factors) and is highly effective, even into later expansions. Mage is more of a supporting toon, adding in pet toys and supplements focus effects from summoned items early on. Mage dps alone is incredible early on and you can even add in the ability to charm in later expansions, but trying to control 3 charmers at once is really difficult and dangerous. Although, casters are very easy to box and if you use timers you can do it if you are proactive and are always anticipating the random breaks.
I tried this before and it is doable, but warrior requires a lot more concentration to tank effectively than say a knight class, which I believe someone else has already said. I love druids for a box team, because they are so versatile and you can still add classes with abilities that mirror, because a druid's redundancy clauses still help a great deal instead of being ineffective. I would highly consider a haste/crack buffer instead of a mage. The beauty of a 3 box crew with a tank and at least 1 heals YOU can trust is that it is very easy to find other people to fill the DPS roles. You could do a bard, which adds in the ability to crack, haste, slow, something else and you can do it while leaving him afk with melody on. This would allow you more time to concentrate on tanking with the warrior.
Enchanter, warrior, cleric... huge dps with charm, solid tank, amazing healer, CC and slows.... Its called the EQ trinity for a reason
The "best" trio really comes to what you want to do right. Are you going to LFG with your trio or is this troop its own mini group? Also how good are you at boxing? War/Dru/Mag offers no real synergy. War (Tank only) Dru (Track, Heal, SoW, Port, Snare) Mage (Tank or DPS + free eats) Above posts have great 3 box philosophies. As a basic rule I would not box a warrior with out a shaman or chanter. Warrior's only really let a single group tank something that would otherwise deal too much damage for a knight to handle. How often will that happen to you? SK/Dru/Ench = Puller+Tank / Heal+Port+Track / Slow + Haste + Mez + Charm + Breeze. 1-SK will not lose agro on a single target. 2-Enchanter slow will nearly double how long you're druid will be able to heal. 3-Enchanter calm/lull spells with FD almost guarantee single pulls. 4-If you fail to single pull you can mez/charm an add. 5-Clarity means the druid can heal longer and will be less likely to be OOM if you need to succor. 6-Enchanter mez/stun/mana drain means that you have a way of dealing with healer mobs. These are the 6 reasons I can think to change up your setup but if you'd have more fun with war/dru/mag then play that. Also if you plan on being LFG it will matter less. As an alternative to SK/Enc you can do Pld/Brd any combination between. tl;dr SK/Dru/Enc offers more bang for your buck.