Geelas is the least controversial to me but even then the G could be hard or soft! I kinda like letting people decide for themselves how to pronounce names though. Adds an element of personalisation.
I thought Gillas was the least controversial, and by controversial I mean the least likely to be confusing as far as pronunciation.
I know for. myself, and this is totally personal opinion, but it doesn't matter what the author puts at the front or back of the book, I will pronounce the names however they seem right to me. I won't spend a bunch of time looking for a pronunciation page.
If you're wanting it to reflect actual Irish Gaelic, the correct pronunciation would actually be Gil-uhs, with stress on the first syllable. (I'm learning Irish, but am no expert). Of course, since you're writing fantasy, you can make it sound however you wish in your world.
Please, write the name you were thinking about, the way you would write it in the story. I think many people will pronounce it differently, and you can change the way you wite it by seeing what are the answers you get.
Great names, though!
Orior