Easiest to use imo for leaves, sticks and big stuff is a
venturi type vac. You can make a powerful one like my
Muck Mop. Or buy one from any pool supply that's powered by a garden hose. They're
very cheap but you need a
pole too. So around $40 total. Power depends on hose pressure.
Even low power will work, you just have to move slower. These work by creating a current and if you move too fast the current doesn't get a chance to setup properly. Because moving slow is a good thing they're very relaxing to use as long as you have the time.
You generally can't see what you're doing because the muck on the bottom gets stirred up so you just kind of move in a pattern until you're happy. Nothing in the bag means you're done. The stirred up muck settles back pretty fast, few hours, 24 hours max generally.
There's no heavy lifting as it can be dragged out of the pond. The water drains out of the bag so it's pretty light. Or it can be dragged to wherever and dumped.
There are some venturi vacs that pump the water out of the pond which don't work very well at all. Been around for years but they keep changing its name. Latest name is
Muck-Vac which they kind of ripped off from my Muck Mop imo.
Pro Sucker is another one I'd stay away from.
I'm not a fan of any of the shop vac type vacuums for most cases.