For Competitive Battling
Let's compare them stat-wise:
-Vital Spirit (DW)
-Solar Power (DW)
Electivire is an OK Pokemon in my opinion. His stats are pretty good, but my beef with it is its limited movepool and near useless abilities. While its movepool is not at all bad, his attacking stats lean much more to it's attack stat than its special attack stat, why does this bother me? Simple, Electivire is an Electric type, meaning the majority of its moves are made up of powerful special attacks, and mediocre physical attacks, and this does not synergise well with its previously mentioned statistics. Because of this, Electivire stuck with weak electric moves such as thunder punch and wild charge. He also has powerful special moves such as flamethrower and focus blast, but its mediocre SpAtk stat limits their useability.
Don't let his Cons fool you though, as his apparent shallow physical movepool is quickly made up for because he can learn the highly coveted Earthquake, providing him with the reliable type-coverage that this powerful ground type move is oh-so famous for. Also, one can't deny that dastardly attack stat, 123 is not too shabby in the slightest. His defencive stats aren't too shabby either, and while both Electivire and Heliolisk have pretty much the same special defence stats, Heliolisk has no hope of surviving a neutral physical attack, unlike Electivire.
Heliolisk is also a pretty good Pokemon, good sweeping stats, kickass abilities, and a great movepool. While Electivire has a lot of small flaws, Heliolisk has two big glaring flaws. 1: He is incredibly frail, in the defencive department at least. 2: He has an unnecessary secondary typing - Normal. The Normal typing added to Heliolisk doesn't make life any easier for his already poor defences, as it provides only one thing - a weakness to the ever-popular fighting type attacks.
Now onto the good stuff. Heliolisk has three incredible weather based abilities, two of them can be activated by himself via rain dance and sandstorm, unfortunately he can't activate solar power because he can't learn sunny day, but this is no problem as he doesn't have the defences to setup anyway, and the weather effects should be induced via other weather-inducing Pokemon. Heliolisk is a specially offencive electric type, meaning that (unlike Electivire) he can take advantage of his powerful special movepool. He has access to powerful electric moves in thunderbolt, thunder, and can even scout using volt switch. But the fun doesn't stop there, he can learn other powerful special moves such as focus blast, dark pulse, grass knot, and you could even take advantage of his secondary STAB and go with hyper beam if you want to.
Electivire can cover his weakness with ice punch, but Heliolisk does it better with surf, because it is more powerful, covers his ground AND fire weakness, and takes advantage of rainy weather (assuming you're using dry skin for Heliolisk), since it can learn surf, it is also useful to a degree in-game as well.
If I were you, I would choose Heliolisk as your electric type. Why? Because a quick glance at your team reveals that you have physical and mixed attackers, but no special attackers, so Heliolisk will make a nice fit. Just keep him away from things that like to punch and kick, that should be Scolipede's headache, since he has a 4x resistance to fighting type moves.
Sorry for the long post! I tried to be informative as I could!