Phoenix vs. her collar

I got two new kittens a while ago, and I adore them. They were foster sisters, and we couldn't bear to seperate them. They're about 5 months old. Phoenix is a brown tabby, and Munky is a tortie. They're both females.

Well, today I went out and bought them collars with tags. Munky, whose usually really skittish, is doing fine with her collar. However, I can't leave the collar on Pheonix. She does anything she can to get it off, and has even hurt one of her claws getting it caught. We're really worried about her getting caught on it, so we took it off. She NEEDS to get used to the collar because when summer comes, we'll be letting the outside on a harness and cat-run, and she has to do wellwith the harness. I just thought a collar would bea good first step towards it (and is fine for munky). Do you guys have any suggestions for getting her use to the collar? Do you think she'd be better with the harness and should I just use one of those? Would it be a better idea to maybe just sharpee her name and number onto a collar so she doesn't have to deal with the tag? Is there a better kind of collar I can use? (this is a usual nylon safety collar). Is it possible that Phoenix is allergic to nylon? She scartches the collar horribly.

Thank you for your thoughts and ideas!