I like a knife big enough to hold comfortably for a long period of time
A 4" knife is a full hand grip.
The 3 1/2" whittlers are too small for my average sized hands for longer work
I like the blades to be short enough that I can again comfortably use the point of the blade, without loosing control.
I like for the blades to be thin.
I like a Sheepsfoot for the main cutting and removal and has the obtuse end that works well for detail.
A short pen blade is good for digging reliefs.
The split end of a whitter with a coping and pen is excellent for small litte work with smaller amounts of cutting
If find carbon blades do not hold an edge as long as D2
Carbon gets very sharp but the drop off to dull is to quick
D2 does not get so wicked sharp but gives me a good long holding working edge
So:
Queen Half Congress 4" in D2
The knife shape is long enough to hold comfortably and the belly is good in the hand
A single spring so the blade are thin
The Sheepsfoot is thin and short, big enough to remove waste and easy to use the end of the blade
The pen has nice swedging so the point is sharp and strong
Queen Split-spring Whittler 3 1/2" in D2
The main blade is on a double spring and is quite thick, to thick for wood removal. Perhaps if I convexed this blade it would work better.
Th knife shape and size is too narrow and short to hold for a long time
The end with the two blades work well for fine detail where you do not have to push or press hard
Non Slippy carver is a Scandi grind fixed 2 1/2" fixed blade and a 4" wooden handle with a curved blade