The neatest autographed book I've got is John Steadman's 1958 history of the Baltimore Colts,

Neatest one I own is a signed copy of Morris K. Jessup's The Case for the UFO, a fraudulently hand-annotated (not by Jessup) copy of which spawned the whole "Philadelphia Experiment" mythos at some point after Jessup's suicide. Picked it up off eBay circa 1999 for around $29.

My brother, Dan, modelled his "D" after Dave Stieb's cause it was cool. For a time I was bitter my name didn't start with a "D", cause none of the autographs I got had a cool looking "N" I could emulate.

You know who signs a helluva autograph? Sir Jackie Stewart. Google Image Search it. Looks like calligraphy straight off the Declaration or the Magna Carta.

I blame my horrible penmanship on my left-handedness.

i had a helluva time learning penmanship as a kid because of this. i had a very good teacher who was patient with me, but it was still hard. eventually i moved over to printing when i had to write by hand. i decided to try writing a sentence or two in cursive just now and it looked pretty awful.

this guy had trouble with penmanship too.

Penmanship: why everybody remembers John Hancock, and nobody remembers Geo. Hopkins.

The worst signature is Willie Mays. Not because it's unusually illegible, but because he so often writes it upside down, sideways, or any way other than in the normal upright position. I handled about a dozen autographed Say, Hey!s when I had my book shop, and only one of them was signed upright**. It's hard not to believe that this isn't a deliberate act of contempt on his part, or at best complete indifference.

The companies that represent Willie Mays have started to put forth a disclaimer at all of his autograph signings. Something to the effect of "We are not responsible for any damage Willie might cause to your item". An acquaintance of mine is getting every hall of famer to sign a poster... it is quite impressive. Willie proceeded to sign his autograph right on top of Cal Ripken's autograph. Not only that, but he paid around $250 for that privilege.

I have obtained about 25,000 autographs in my life, though my collection has recently been narrowed to just White Sox autographs. While there have always been a few players that scribbled their names, there has definitely been a downturn in the quality of the average signature in the last 20 or so years. Up to and including the 80s, the majority of players had somewhat legible, or at least interesting autographs. Now there are probably no more than 5 guys per team that have nice autographs.

Some recent guys that have nice autographs: Torii Hunter, Michael Cuddyer (there's that Killebrew influence mentioned upthread), Ugueth Urbina, Jeff Keppinger, Mariano Rivera, Pat Neshek, Pedro Martinez... can't think of any others right now.