There are also other Pokemon that are generally useful, such as Pillage (a defensive tank with many resistances and good attack) and Petraflow (which is one of the best counters to Infernox until Water/Light types like Jelluminous are released, as well as having access to attacks like Ice Beam). However, I will say that there is no 'best team'- no matter how you build a team, where will always be a combination that can beat it. Many teams prepare for as much as possible, but still have weaknesses or coverage gaps. So teams will most likely be partially personalized, with coverage and backup to fill in the gaps. @TD: Valkeran can also be used to revenge kill Pokemon such as Petraflow, Slagtite, and weakened Nucleor and Cosmite. Valkeran is kinda frail with its various weaknesses as well as having average type coverage, but it can counter some important Pokemon with fast Speed and above average Special Attack. I wish Valkeran had Leech Seed access though...

Using Pillage, Mechasnap, and Valkeran on the same team would be a bad idea. Not only does that give you a triple weakness to Fire (which makes your team very vulnerable to an Infernox sweep), Mechasnap doesn't assist your team at all since Pillage already picks off Pokemon such as Slagtite and Caribuck with Flash Cannon. Mechasnap should be used when you don't have a Steel type but your team lacks Speed instead of Defense, while Pillage is good if you're lacking crucial resistances and need something bulky. I recommend developing your team further and dropping one of those Pokemon depending on what you need.

Ok. So my party should be Shusk, Infernox, Squiquil, Pillage, Shiny Slagtite (gonna evolve Dribbik), Valkeran (or shouldn't he be included?) and... who else would fit? Would Triantuslash be a good choice?

Missing Seuiquil but my team is strong with Infernox, Valkeran and Reagle

Don't include Valkeran and Shusk on the same team - they pretty much get the same things. Shusk is more defensive with a useful Fighting (and Normal) immunity and can take on Electric types better, so you really don't need Valkeran if you're using Shusk. I'd recommend something that has good speed for your team. Reagle would work, since it can also give your team a Ground Immunity. If you do this, you should get something with a Rock resistance as your seventh. Your offense is there, but you'll need some more defense. As it stands, your entire team is weak to Rock, and none of your Pokemon can really take a strong hit. You'd need to develop it a little more for me to give a suggestion though.

Squiquil can win against a rock type. Maybe adding Junzu won't be a bad idea. He is good against rock types.

It can because the rock Pokemon you find now are wild Pokemon. Once competitive battling is in, Spiquill won't be able to defeat Sp. Def. trained Slagtite easily for example.

Valkeran is ok on the same team with Shusk, and you have Infernox to support this. Infernox takes out two of their main weaknesses instantly. Slagite takes out another weakness. Just add a psychic pokemon and you'll have eliminated all weaknesses (besides Shushk's weakness to ghost and dark). Psychic shares a common weakness with grass, so again, Infernox compensates for its weakness. You pretty much just nead a psychic pokemon and thats it. Pillage is useless, since it's strong against grass and psychic, so Shusk and Infernox are strong against the same things. Pillage can be replaced with a fighting type to fight normal type pokemon.

Marog, Valkeran, Hartoom, Stritus, Astroidus, Diabra and Nucleor was my old team, anyone wanna give a little critique on it?