Marc
Very good to read that you are thinking about pencil poppers. They are so neglected by many GT anglers these days.
For the long type, my personal favourite is Adhek Ocean Lady. This is a very long lure indeed and it has great record of catching big GTs. Added to that it, buying a few will not break the bank. Casts extremely well and has a very dramatic skipping action, perfectly imitating a fleeing long tom.
I also like using Craftbait GT Pencils which are a bit shorter but still quite long. Somebody told me these are not being made anymore - no idea if that is true but in any case you should be able to find them.
For the shorter, stubbier type of pencil (sometimes called tuna pencils it seems), then Carpenter Kattobi 145 is a very nice lure indeed.