This is an old question but I keep looking for decent clients, so thought this might be helpful as some of these answers are outdated

NATS CLI should be the go to tool, it pretty much has everything you need.

There is also NatsDash if you are looking for a UI/GUI/TUI based tool for managing or interacting with core NATS or Jetstream consumers: https://nats-dash-gui.returnzero.win/ it works with existing NATS CLI contexts.

There is also NUI which is web based, but it takes a quite a bit of configuration to get it working.