I like Lancel. In fact, I like it a lot more than
Lance (just not a fan) or
Lancelot (okay for legends, not on a modern person).
Lance can be a nickname if the bearer wishes it to be so.
On the other hand, I think
Galahad is fine as a full name. It's a legendary name (which I like) but not as obvious or well-known as
Lancelot. Galad is better as a nickname; on its own it makes me think of
Galadriel for some reason.