Because boarding only works at all if you have an enormous speed advantage, it is really only useful against commercial ships, disabled ships, and space stations.
For the first two, you still want enormous speed, because getting a ship all the way to zero speed risks destroying it. If you have mostly crippled an enemy ship, it will likely be separated from their fleet, and therefore have less point blank fire power. If you want to be safe, you can send a sacrificial 80 ton scout to check, but otherwise you are going to have to enter their envelope. A tactic is to bait out their firepower at the edge of their range envelope, and close before their weapons can recycle, but that isn't going to protect against point defense shredding your boarding ship.
A lot depends on what you know about the enemy ships. If they are dedicated missile combatants, you can just wait until they are out of missiles, or if they are on a 10 minute reload cycle. If they are a beam combatant or mixed with integral point defense, you will have to risk losing boarding pods. So the question is what are the effective and efficient ways to boarding, losing the least boarding pods? Numbers? Armor? Speed? ECM? ECM, unless you have a significant tech lead with it, is an expensive way for a fighter or FAC to defend against a capital ship. ECM and numbers might work, if the target has a limited number of ECCM to apply to whatever is swatting the boarding pods.
Speed is going to help a bit more against missiles than point defense. But being able to soak AMMs is going to increase the number of missiles required to disable more than pure speed is likely to. A solo disabled ship isn't likely to have the missile density to penetrate the point defense that railgun fighters escorting the boarding pods can bring to bear. Unless you are talking pvp, where the player will hold fire until point blank to bypass PD.
On a pure cost basis, I would generally prefer a speed + armor solution. And it would also depend on whether I was more limited in shipyard capacity or marine companies.
Another solution is to have the boarding modules on your fast beam combatants, in cryo modules. They are already fast, already close, and already have the armor and/or shields to be survivable, especially vs a disabled ship. Having non-cryo boarding pods on fighters or FACS is great where you want absolute speed, for going after intact commercial ships, where you couldn't afford that engine ratio on a beam combatant.
Boarding a space station, the calculus is slightly different. You can cross a point defense envelope before the enemy fires, and then all you lose is the boarding pod. So cheap boarding pods would be the efficient method there, and possible have a ship at the edge of its main beam envelope drawing fire as the pods approach.
I don't see stealth boarding pods working by themselves, so evaluating them depends a lot on your doctrine of who they are working WITH. And on whether you are talking about fighting the AI, or fighting in duels. Or whether you want anti-player designs for RP purposes.
ECM helps most (in my opinion) in combats where both sides are using similar ranged weapons. It can help you get off the first shot in a missile duel, or more effective in a beam engagement. However, unless you can close the entire enemy envelope before it runs out of missiles or before it can reload, ECM isn't going to help beam ships much vs missiles, or a boarding pod versus beams.