I've been wondering why people invariably suggest Excalibur (if they voice an opinion other than 'Any') over Mag and Volt so consistently. Usually the reasoning is "Excalibur is harder to get in-game" or "Excalibur makes Junctions super-easy" both of which didn't make too much sense to me.
Excalibur is at Ceres, less than 1/2 way through the Star Chart, and only 1 planet further than Mag at Phobos (I don't count Mars after Phobos, I count it before Phobos, and I don't count the Void, since it's 3 nodes, and has no Junction)
As far as the Junction Specters are concerned, Mag can cheese those just as easily as Excalibur - Magnetize the Specter, then put bullets or arrows into their head, or better yet, a projectile with punch through.
But I learned something when a Warframe video autoplayed on Youtube. Pre-PoE (more or less) all the Warframes had different drop locations and Excalibur was in Uranus or Pluto. No wonder veterans thought he was hard for newbies to get! He actually used to be harder to get! Granted, it's easy-peasy now to get him in a new game, but yeah. Once upon a time it wasn't.