1. CatPVP

They have the best regional coverage (NA, EU, and crucially, ASIA). If you’re playing from Singapore or Australia, this is basically the only place you can play with a double-digit ping.
They recently added an ELO system to move away from just being a "practice" server. It’s okay, but it still has lots of cheats
Pros: Big player base, instant queues, niche kits (Cart, Spear).
Cons: Closet cheaters

2. FlowPVP

The Tech: Proprietary server software. They’ve done a lot of work on their hitreg and kb to make it feel less clunky than a standard Paper/Spigot server.
The Ranking: Very clean ELO system (Bronze -> Grandmaster style).
Pros: Clean UI, better matchmaking algorithms that actually try to prevent smurfing, and a generally "sweatier" but more professional community.
Cons: If you have 70ms, you’re still going to feel that 70ms "delay" when you click. Very new server

It uses P2P with UDP netcode. If you and your opponent both live in the same region, you get sub-10ms ping because the data doesn't go to a central server—it goes directly to your opponent. It handles packet loss like a modern shooter (no lag-backs).
The mod-based Logic/Heuristic system is probably the most effective AC in the history of the game.
Pros: Best "feel" by a landslide. If you play Crystal or UHC, the hit-reg feels like you’re playing LAN. Uses Openskill, which is more accurate than ELO. Very good replay system.
Cons: High barrier to entry, currently closed beta, not released yet.

You can be on your own favorite SMP or a practice server and queue into a ranked match. The system then spins up a "Temporary Server" geographically located between the two players to make the ping as equal as possible.
Automated Tiers (LT5 -> HT1). It’s designed to replace the old McTiers manual testing with an algorithm so "tier-testers" can't gatekeep players they don't like.
Pros: Player count. It's backed by Dream and Donut, so the player count is going to be massive. They're trying to expand it to eSports.
Cons: Probably still lots of cheats