In terms of lower school, Hecky grammar is pretty solid, but I have heard others suggest that it's mainly because they choose smarter students using the test, and so they tend to get better GCSE results.
I went to Greenhead for 6th form, but most of it was during lockdown. The 6th form at Greenhead is very big and (at least for chem bio and maths) the departments are well organised - each subject is split into topics and units, and each unit has a content booklet, question booklet, and exam practice booklet (they call them packs). I have friends who went to HGS 6th form and I heard it was pretty bad - full timetables, overpriced food, lack of space in the Jo Cox centre, bad covid planning etc. IDK about Hudds new college though, but theres a high chance you'd be better off going to greenhead or hecky instead if you can.
Greenhead food is nice - its a short walk to hudds town centre where you have kfc, sainsburys, greggs, costa, mcdonalds etc, hecky is a bit dead so not much choice.
Greenhead is much bigger - 1000 students per year, so the support per student is lower in quality, but the teachers are all nice and friendly and you can just go and speak to them if you need help or anything. Facilities: the science labs at Hecky are nicer than the ones at Greenhead (only marginally though), but I would be very surprised if hecky had anywhere near the amount of extra curriculars as greenhead.
IMO just go greenhead
, most of A levels is based on your ability and not the school reputation.