For carving necks these little chinese spokeshaves are my favorite. Cheap, light and work like a charm. Take a little work to set them up properly but when they are...smooth like butter.
Of the Stanley you mention I have the 51 and a newer one similar to the 151 with the double adjustment knobs. If I can judge their prefered statis by the one that I will grab first every time it's the 51. I find the 151 kind of top heavy and as I hold the spokeshave lightly, it just feels awkward and unbalanced in my hands. I've had it flip over and ding the neck more than once. But that's just me and others might have a different technique with no problems.
I forgot to mention the other metal spokeshave I really like is my old Record 64 with the thumb screw fastener. You can usually find them for 10 bucks or less...good value.
I'd say your choice of tool should be based on your own experience and practice. I don't recall ever using a spokeshave, but I've used pretty much every kind of rasp along the way. I do like those handmade ones, whether Eastern European or Chines - they are really sharp.
That said, my favorite tool for necks is a regular draw knife. I'd always figured that the Martin catalog cover photo of the guy whittling a neck with a draw knife was a staged thing, not what was practiced in the Factory. When I first visited Nazareth, I was surprised to see a guy shaping necks just as in the photo. In fact there was a row of neck makers doing just that - taking the shaped blank and finishing the carving with skill and ease.
That inspired me to break out my old draw knife, sharpen it up and practice so I could make the wood melt away as I'd seen them do it. . .
Another vote here like Rusty for the stew mac dragon rasps. Until I read this thread, I had completely forgot I have a very nice Lee Valley spoke shave that I never use. With such good rasps, the spokeshave seems a very course tool now. I never did like that now & again the spoke shave would want to run with the grain and start cutting too deep or cause chip out. This is never a problem with the dragon rasps. One of the best hand tool purchases Ive made in a while.
Wow! Interesting how many use the dragon rasps. I've got some but don't use them except around the heel and neck/head joint area.
I got used to the little chinese wooden spokeshaves years ago, learned how to set them up, how to use them to avoid chip out and so on and cannot think of anything I'd rather use.
I agree with Frank though, the tool you use should be what you are comfortable with and have experience using. Don't use something just because someone else does. I, for example, would not touch a drawknife to a guitar neck. I've seen the builders in Mexico and Spain using them to carve a neck in what seems like seconds. Impressive for sure but I can guarantee you, not nearly so impressive in my hands.