First of all, very happy to see myself having to update the scoreboard more often this month. This game appears to be a hit!
All the talk about Lightning vs Vulcan inspired me today, what if I did a nearly all-Vulcan run? Well I did, and this is what I got -
ExedExes - 4,438,870 - 6-1 - MAME
This was I'd say close to a 90% Vulcan run, only stopped when I had to pick up the lightning in Stage 4 due to either taking that or my life/less points. I switched back on Stage 5 and kept it through there. See the points despite the better forward progress? If I was using lightning, I'd have that score by the time I reached Stage 5's boss, I'm pretty sure. I'd also say that having my X-Arcade stick back also helped somewhat. If only I was able to repair it sooner, I'd have done better on other SOTM games this year, I'm sure!
Lightning is great for additional point scoring, especially on bosses. 4 mil by Stage 5 exclusively using lightning is no problem. However, I am finding to like the Vulcan, because it not only has a couple of smaller fireball-like shots towards the middle among its wide bullet spray, but the bomb truly cancels ALL shots on screen. The lightning bomb's blue lasers only cancel those bullets the lasers come in contact with. Also, another weakness is described by the poster above me -- the fact that it can only concentrate on one enemy/a set of enemies at a time, while everything else that's still alive can kill you. If you want points, lightning is the way to go. If you want to see Stage 6, go with the Vulcan

Mixing them up may yield a better result.
Knowing this, I am gonna go back to another all lightning run and see if I can get to 6-1 with a better score.