It's time for the world to know (or just be reminded) of my preferences.
Ground : The type of the Earth. Seriously underrated type, having 2 resistances (rock and poison) and 1 immunity (to electric), Ground could ask for more on the defensive side. Offensively it's one of the best, wrecking teams, as 5 types are weak to it, and even if a flier appears, Ground types usually have a good movepool to get rid of them, mainly Rock and Ice type attacks. Another thing that adds to the type is the great variety it has. Most people think immediately of bulky pokemon, mostly used as tanks or walls like Gliscor, Hippowdon, and Quagsire, when speaking about the Ground type. However one can also find great supporters like Swampert and Garchomp, some fast sweepers like Excadrill, the vicious Landorus bros, and Krookodile, or just heavy hitters like Golurk, Diggersbytho and Mamoswine. And of course, who can forget his majesty, the one who knows all, the unstoppable (under certain conditions) powerhouse Nidoking is?
Naturally, Ground itself has a shortage of good moves to exploit, mainly having to deal with Earthquake and Earth Power for both the physical and special side of the competitive attacks. Fortunately it has a vast array of moves to use, thanks to the many different secondary typings, and the fact that Ground types essentially have to learn moves from other types to compete.
Being immune to paralysis outside of Body Slam and Glare is a great way to sweep, and even if you didn't, the generally good defensive stats guarantee you wouldn't go down without dealing some serious damage yourself.
Funny thing is that the current megas Ground has are few and do not help the type as much as it needs it, but they sure can destroy the enemy teams given the chance. Just take a look at Camerupt after 2 Rock Polish, or Garchomp with the adequate paralysis support.
We need the following type combinations: Ground/Fighting, Ground/Bug. Ground/Dragon, Ground/Fairy, and more of Ground/Dark and Ground/Ghost
Next type is Steel. Those little pesky things define the metagame with their presence in both defense and offense. Actually being so sturdy just thanks to their type, almost always guarantees problems for your opponent. Weak to the most major offensive types (fire, fighting, ground), they know they should have serious reasons to stay in the game, and they do with their great amount of resistances (and an indifferent immunity to poison). Nerfed to not be able to stop Ghost and Dark anymore, they lost a bit defensively, but they gained a lot offensively, being one of the two only threats to the new menace of the meta, the fairies. Truth be told, Steel benefited more from the Fairy birth than Poison, mainly because it was already a good type to use and, compared to the Poison type, you have more pokemon to work with. Don't judge me wrong. I adore the Poison type, but I feel that they were not treated as equals, being given mediocre movepools, lower base stats, and few secondary typings that could help bring them into the competitive without having to rely on certain niches. Steel didn't have that. Some Steel pokemon rely on their brute strength and sturdiness to survive, while others are complacent about their mediocre-to-good base stats and good defensive typing to go all-out and wreck havoc.
Steel types can serve a multitude of roles, and the most fascinating thing is that the same pokemon could play different roles based on the team it's in. Certainly things like Ferrothorn, Bronzong, Skarmory, and Empoleon are more passive players that may deal damage based on the occasion, but you'd also look at Heatran, Aegislash, Scizor, Aggron, and Metagross, that can work defensively at one point, be a scarfed sweeper at another, or just go crazy, pull of a mega evolution and decide to finish with your team a few turns earlier.
We need the following type combinations: Steel/Poison, Steel/Fairy, and more of Steel/Water, Steel/Fighting
Third type in terms of fondness could only go to Rock. Underrated, ridiculed, cast away by those who cannot understand the power they hold. Certainly they come along with many weaknesses that vary, so they can never feel safe. Sure, there are few Rock type pokemon that can stand their ground against the vast majority of the metagame being able to land a Super Effective hit. Definitely, I have not forgotten how few of them are seen in the meta, and how some repeat themselves. However, there is no team without a Rock coverage move, and multiple Rock resistances. Funny how the type used the least in the meta (even behind Ice) is the one every player fears the most. Even funnier is how, through all generations, they didn't dare give Rock a strong move with perfect accuracy or one with side-effects that lower stats, much like every other type has. Up until now, only 4 moves are viable for competitive (2 physical, 2 special) with the 2 special ones being so scarce, you won't even see them unless you battle a Diancie or a random HP-Rock.
However, Rock has it's quirks that bring its abilities to the frontlines and make monsters like Tyranitar, Terrakion, and Aerodactyl, look even more fierce. Basic source of badassery; the sand. I hope nobody forgets how Rock types get a 50% boost in SpD when the sand's up. If Tyranitar was not so weak to Fighting and Earthquake was not so common, you would not dare face it in the sand, especially since its other weaknesses are more often than not, not STAB boosted, therefore not guaranteeing a kill.
Moving on to the next best thing that makes the type cool again, and that's no other than the one, the only move almost guaranteed to be seen in every single match. No I'm not talking about Hyper Beam, you genwunners. It's Stealth Rock. Yes, the move that's wrecked so many friendships and makes Fire, Ice, Flying, and Bug types think twice before entering the scene again is of the Rock type.
Speaking of Rocks, yes there is the problem that they are also underrated as a type and many pokemon could use some better stats or movepools to be better in the competitive, and being given a wider selection of secondary typings would be great, since they can use them to a full extend. Even so, in the lower tiers you can make use of walls like Cradily and Gigalith, man up and attack with Armaldo, Tyrantum and Rhyperior, or just sweep the floor with Aerodactyl and Barbaracle.
We need the following type combinations: Rock/Electric, Rock/Ghost, Rock/Poison, and more Rock/Fighting, Rock/Bug and Rock/Flying
Notes:
1) I am well aware the types above benefit most from Sand teams
2) Forth place goes to Poison, Fairy and Psychic, even if the top 3 are just minor preferences over the other types. I love all types equally. Except for you, Ice.
3) The Zygarde forms are going to Rock, shake the Ground, and be hard as Steel