Let me rate the anti-vehicle options in order of effectiveness, from least to most.
Edit: Whoops -- I should mention that this is assuming that the enemy armor is piloted by smart, TG people. Pubbies can be easily taken out with ... ah heck, any number of things. A support's EMP lock is probably the easiest.
But, assuming smart people are working against you:

1. Least effective: engineers. They don't inflict damage quickly enough, and are easy to kill. Most pilots fall back and repair after taking damage ... making engineers a deterrent at best and free tickets for the enemy at worst.

2. A tad more effective: CO EMP/OS. People like to blame others for their own failing: blaming a CO for not taking out enemy armor is the #1 way people reap self-righteous moral high-ground from a bad round.
The truth of the matter is quite a bit more ugly. Taking out walkers is nearly impossible without a prior EMP grenade on walker.
And taking out anything else is a waste of time because it either spawns too quickly (read: APCs and tanks -- usually a 60s spawn), or is piloted by someone who knows how to keep moving or look for the EMP shimmer.
Again, the CO's tools are highly over-rated for their anti-armor capabilities. At best, the EMP/OS is a quick bandaid patch for a team that has lazy or not-very-smart squad leaders.

3. Same rating as previous, but a bit higher because it can be executed by anyone: buggy doom.
Buggy doom without EMP grenades is "free points for enemy armor." Buggy doom with EMPs against walkers/tanks is effective, but APCs is difficult. APCs can accurately and easily damage FAVs at range with the F1 seat and can also EMP the jeep.
Against APCs, best case scenario is to get behind them and fire 2 Pillums simultaneously.

4. Recommend method, far surpassing all of the previous: friendly armor squad.
Least used method because people would rather complain about any number of things instead of taking matters into their hands and constructively contributing. Friendly and enemy armor keep each other in check.
If there isn't an armor squad up on your side, start one. If there is one, help them by taking important flags. For example, on Belgrade, take Statue.

5. Same rating as previous, but a bit higher because it can be executed by anyone: taking strategic flags.
If, as an infantry SL, you're able to capture the enemy armor spawn flag, the problem is gone. This is why Berlin Outpost cap is looked at as a hallmark of a good SL -- it removed the Rape APC out of EU's hands. Also takes out the EU CO's assets and allows your armor to breathe a bit easier.
If removing that spawn is not possible, then consider other strategic flags.
On Suez, take all flags and then watch the 18 000 PAC tanks obliterate your armor-less EU team. Or capture Inner alone and let your gunships destroy the rest of their armor with impunity.
On Belgrade, take Statue. This grants you the walker and that alone has huge anti-armor capabilities. Also, it grants your armor high ground.
Also a possibility, though a bit worse -- take the first flag out of enemy UCB. Works well agains the Belgrade PAC because the Pond rorsches are absolutely killer to PAC armor.
Also on Belgrade -- try not to hold Comm Tower if the enemy has the flag immediately next to it ... this is prime shelling ground for APCs and tanks.

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[blantant self-promotion]
Also, if you hate dying to APC mortars -- you should consider attending this TGU class I'm running on APCs. I'm hoping that'll help you figure out how APCs think, and then you can outsmart them, and have an evil little laugh while stroking your pointy French mustache.
[/blatant self-promotion]