If you start collecting county tops in the north it seems simple enough, you climb to the top which is obvious in location!
In the south many tops are very ill defined. It is a big advantage to put a POI. into your GPS using the grid ref from hill bagging. Most are in areas of good scenery.

There are several tops in a large area contour ring with vague bumps anyone of which could be the top. I would settle for the hill bagging grid ref on the nearest right of way.

Surrey is very clear, has a tower, and is named as the county top.
West Sussex has a trig point but the true top is alleged to be a few metres away in the undergrowth. The Trig Point will do!
East Sussex is a nice top.

Kent is in a garden. Go on a sunny day and someone will be out and will invite you in. A no go if there is no-one in. The entrance gate would have to do.
Cambridgeshire seems to be a waterworks structure but this is artificial. The owner of Hall Farm B & B, Chishill Hall reckons it is on his land south of the farm and proud of the fact, but not keen to have people roaming through his wheat. I think the spot height on the road is the best bet even though it is not the top. If you stay there the bedroom is higher than the waterworks structure!

Essex. Another vague one but the path is very close.
Suffolk. See Essex! The bus can drop you nearby and there is a nice walk back to Bury St Edmunds via Ickworth Hall. Uses an accessible section not marked as a right of way
East Suffolk is on a military airfield and is best ignored.
Herts. Spot height on road. Johny Muir’s book seems to have it wrong.

Bucks. A marked boulder! It is probably not the highest point but it will have to do. You need a POI. as the clear paths to it are not marked on the map and the Forestry Commission is re-arranging the landscape to cram more cars in so as to increase CO2 emissions.

Oxford. Bald Hill on the OS map is not the top. The top is in a wood to the south and you would be lucky to find it without a POI.
Hunts. I have not been there but see Essex.

Middlesex. Hill Baggers and Johny Muir’s differ on location. I would go for Hill Baggers. It is a Hert/Mddx boundary post on A4140. It is a surprisingly nice walk from Bushy or Watford High St station, mainly through field with dramatic views.

This may be a complete list of vague summits but I hope others will add information helpful to other baggers.