I have 35 ft-er (wing keel, 1.5m draft). Places "wot I have anchored at" include:

Alde, near (& downstream of) AYC.

Butley, just before ruin/jetty

Ore, Abraham's bosom
Ore, SW of Havergate Island
Ore, 1/2 mile up from entrance (speed boats can be a nuisance, though)

Deben, Rocks (& opposite shore)

Orwell, W. shore, just up from Shitley Spot
Orwell, W. shore, just south of Fox's (only briefly, to visit boatshow)

Stour, Erwarton Ness (& opposite on S. shore)
Stour, upstream of Erwarton Ness on N. shore near school.

Colne, E. shore upstream of Colne Point (good in Easterlies)
Colne, by Bateman's Tower (good in Easterlies)
Colne, Pyfleet
Colne, E. shore, upstream of Pyfleet

Blackwater, S. shore, downstream of power station
Blackwater, N. shore, downstream of Nass Beacon
Blackwater, N. shore, inside of Thirstlet spit
Blackwater, S. shore, upstream of power station, outside Pewit Island
Blackwater, S. shore, Stansgate Point, by Marconi S.C
Blackwater, N of Osea Spit, near Goldhanger Creek
Blackwater, S of Osea Island, up & downstream of Osea Pier
Blackwater, SW of Osea Island, upstream of Doctor Buoy (& opposite shore)

Temporary anchorages:

Just SW of Gunfleet Lighthouse (2 hrs, while we explored LH)
Just N. of Raysand Buoy (1.5 hrs waiting for water to enter Crouch)