I use a few different digging tools that have been modified for the various types of detecting that i do,the main theme that i use is a Ash handle stainless steeel border spade that is cut down width wise and length wise and also has a point on it as well,so that it can really get into hard baked clay ground during the summer,the ash handle lasts years and overal the spads are pretty light.
The heads are cut to various sizes mainly as mentioned above for what ever detecting i am doing on the day,if its say after a hoard then a bigger profile spade head would be used,always carry 2-3 spades with me just incase,its sods law that if you have travelled miles to a special site bank your spade handle can snap hence backups.
Prefer a longish handle with a total spade length of 40-42'' so that i dont have to bend over so much,back problems start appearing if i use a shortish handle,after the detector and headphones a decent designed or modified spade/digging tool is very important to me,nothing worse than one breaking when you are miles away on a large farm site and you have to travel back to the car for another one.
Always important that you use safety glasses and guards on the grinder if you are doing it your self,it only takes just one second and you could loose fingers or your eye sight.