Of the two I prefer
Gideon on first reaction, but
Ernest could grow on me (just have to get past the
Bert &
Ernie association!). In fact I might try it out on my list with some combos...
It actually has never occurred to me that
Gideon needed a nickname. Gid/Giddy are not appealing at all. What about
Deon? I don't think it's too contrived.
Gideon Arnold flows better than
Ernest Arnold. But I prefer
Ernest with
Theodora - an interesting conundrum!