IMHO best all around bit for engraving is 60 degree, i prefer it on 1/4 shank.

The 90 degree are good for cuts for folding say Dibond or other materials. Not very useful on signs.

The 30 degree are best for jewelry and most of all for small stamps and very small signs. This is a very needed bit, but its very breakable. Any small mistake and snap..., not good for wood though and easily melting plastics.