Competitive mode in CS2 keeps the classic ladder of eighteen skill groups, from Silver I at the bottom to The Global Elite at the top. In between sit the Silver Elite ranks, four Gold Nova ranks, the Master Guardians, Distinguished Master Guardian, the two Legendary Eagle ranks and Supreme Master First Class. These icons are what most players still mean when they talk about their “CS rank”.
The big change compared with older versions of the game is that a Competitive rank belongs to a single map. You can be a Legendary Eagle on Mirage and a Gold Nova on Nuke at the same time, and each map is ranked on its own. A rank boost on Boosting24 is therefore always ordered for a specific map, with your current and target rank on that map.
Competitive is a separate ladder from Premier, which uses a numeric CS Rating instead of icons. If you care about the rating shown in Premier, order a Premier boost; if you want the classic badge on the map you play most, a Competitive rank boost is the right service. Many players take both, because each mode matchmakes you with different opponents.