Give the Alondite to one of them and they're even stronger. Same power, unlimited uses, only difference is color. The other thing is that after the second battle in the Tower of Guidance, you'll recieve a really powerful sword called the Alondite ((sound familiar?)) Zihark and Mia ((as well as Edward)) can use the Alondite, which is pretty much identical to Ike's sword, Ragnell. Mia and Zihark, on the other hand, are extremely powerful when they change to Trueblade. Zihark, Mia, or Edward - The three swordsmen ((and woman.)) Now only take Edward if he's at least a level 15 Trueblade, he overall isn't very good unless you waste some good items on him. Especially because of the fact that he has Canto ((can move after attacking or using an item)) he'll prove a strong ally. Haar - If he's a Dragonlord, he'll be extremely useful as well. But of course, she's coming along with you. This also goes for Micaiah, make sure that you didn't waste your Purge yet, otherwise she's useless. This will become extremely useful in many ways. Well, only do it if you have any long ranged magic with you ((ex, Meteor, Blizzard.)) The reason is because after hte second battle, Yune will bless all equipped weapons and you've got an unlimited uses long ranged magic attack. Soren - If Soren is at least an Arch Sage, please, please, PLEASE take Soren with you. He's extremely good, but he needs high level, like everyone else.
If you didn't get him to level 5 Marksman yet, I would suggest to not even bother dragging him around. This, though, gets applied to all characters. If somehow you guys didn't realize her power and never got her good, then don't even bother dragging her around. Titania - Titania is extremely useful, Ike will get an Axe called Urvan ((view conversations)) and by giving it to Titania, she'll be ever scarier than before. Many of the Greil Mercenaries will come in handy. Pretty much all of the Laguz kings/queens will become extremely useful from here on out, so be sure to drag them along with you. This decision can be very difficult, so I'll give you guys a heads up on who to choose.
Now you've finally made it to the Tower of Guidance, though you can only choose 11 people ((or laguz.))