I was asking the same question a couple years back when i got my 10"SCT and a number of kind folk universally suggested a good quality 20mm eyepiece.It was suggested at the time a eyepiece of this focal length would be my most frequently used ....and it has been
. I ended up getting a Nagler 22mm Type 4, although I came close to getting a 20mm Nagler Type 2.The 22mm is my favourite eyepiece without a doubt and sticking my neck out i would suggest maybe these two eyepieces or something of equivalent FL.