If you’re asking seriously... tmux has a unique interface which is probably not worth learning merely for the purpose of managing multiple active sessions. You also can’t wire it to accept proper GUI commands with the mac command key. Tabs make sense.

Personally I recommend Terminal.app :)

I'm not saying you have to have tabs, if you want to paint your terminal pink with yellow fonts and render it upside down then go for it, but I'd like tabs :)

I needs to connects to multiple servers at the same time, and tmux sessions shouldn't be stacked. How can I do that without tabs?

If you have 2 tmux servers with different hotkeys you can totally nest them safely. I have a different hotkey prefix for my machine and then leave the default for servers. Works great!

Use multiple panes and/or windows? It's a terminal multiplexer, each panes is a separate terminal, just like tabs.