Let’s start off by discussing what the basics are,
Free-to-play or f2p: A game that has doesn’t have an upfront cost in order to be played.
Examples of this would be: Hearthstone, Path of Exile , Dota 2 and League of Legends
Pay-to-win or p2w: A game where a person can gain a benefit over another player by buying said benefit.
Pay-to-skip: A way to skip parts of the game such as grinding or leveling in order to save time by paying money. The important part is that a person paying to skip content is only saving time and has no other benefit over another player.
Micro-transactions or mtx: A way of buying in-game content piecemeal usually (though not always) in smaller transactions tailored to the specific content in question. These are often designed to be purchased in small amounts by a large amount of players in the hopes eventually sustaining development for the game.
For me any kind of pay to win elements in a game are a big negative, as it means that I am required to pay in order to compete with other players. The worst case scenario is one in which I can in no way compensate by playing more or being better and the player with more money sunk into the game always wins more often than me.