the outsides are usually the first to go, that is the tie rod end closest to the wheel, turn the steering to full lock so you can see behind the front wheel, you'll see the tie rod "pop" up and down when you jiggle the wheel at full lock.
If one side is gone then if the other side looks similar age, I would replace that too cause it wont be too far away from failing as well & saves having to pay for another wheel alignment as well.
Check play on the inners by placing a hand over the tie rod and moving the steering, best done if the wheels are still in contact with the ground, even if slightly jacked. If the inners also have play,instead of buying individual tie rod ends, its cheaper to buy the rod with inner & outers and do both sides- just measure the lenghts of the old and screw the new ones in to the approximate same length and get a wheel alignment done.
Just a word of caution, sometimes they can be very hard to pop out of the steering arms, support the arm with a jack and remove the nut first before trying to pound out or buy a ball joint splitter, which makes life a whole lot easier.