In regards to the poll I think it leaves too little information to answer it. Are you suggesting we streamline SoF and SOL to Merc/Elders membership and they then fight? Do we let those alliances pick and choose who should participate? Or do we double Merc/Elders with present membership/activity? What you mean determines the outcome of the hypothetical war.

If SOL and SoF and Merc scale down to Merc size and fight it out then SOL will win pretty much hands down I will say. The best 17 of SOL are better than the best 17 of Mercs in every aspect of war; walling, hitting, prepping.
SoFs weapons are great stocks and fast kills and those speedkills will be considerably harder to pull off at 17 members than at 40-50 as in recent wars, further they are only 20 players now so they would only get to remove their 3 least active.
SoFs strategy should work a lot better if playing with another alliance, yet that has not manifested lately, for to me unclear reasons. SoF also keeps feeding getafix 1-2k defends every set for no reason. :)

If we duke it out at 30 members by adding 10 similar skill/activity members to SoF and 13 to Mercs it will be a considerably harder thing to call. Same if we scale down the larger tags at random instead of by selection. SoFs prep speaks for them but their speedkill dependency will be an issue again at low membership. Mercs pound for pound walling abilities have historically been unmatched which would make several of them unkillable in a 17vs17 war. Getafix also would not die vs 17. Too close to call in either of these scenarios.

All in all tho right now at present membership SOL would win 1v1 vs any other war tag, which makes them the best war tag.