Don't use Steelix in raids. Off the top of my head budget options (Garchomp and Metagross being better but tougher to come by if you missed their Community Days) are Rhyperior for ground and Excadrill for Steel (or Ground too I guess). Honestly Excadrill is better for pvp also. If I had to pick, first one for pvp, second for raids, so choose whichever you do more of. Scizor is a better Steel mega. There are other types with megas that cover what you would need a Ground mega for: Blastoise, Lopunny, etc. Steelix and Mega Steelix (and Aggron and Mega Aggron for that matter) are very defense heavy Pokémon in a Pokémon game balanced so that offense (and to a slightly lesser extent bulk, which is to say HP) is king. 

All this said I still use my shiny 98% Steelix once in awhile, but that's because I like it and for the mega boost and bonuses, not because there aren't many better options.

I would invest in the PVP one. I don’t think any of them will be much useful in raids though.

Honesty onix and steelix are trash for raids and pvp. Move pools are bad and they’re so slow and too bulky like rhyperior. Go with a garchomp or aggron instead (for mega)

Which to evolve? Main use is in raids and maybe a little bit of pvp.