Christina and Krystal don't look anything like eachother!! Here's a little comparison for all you people who can't see past the blond hair blue eyes similarity:
Krystal's eyes are slanted, Christina's are straight.
Krystal has wide hips, Christina's waist is more "tight".
Krystal has a medium frame, Christina's is definately small.
Krystal has rosy skin, Christina is tanned.
Krystal is tall, Christina is medium/short.
And finally, the biggest difference between them is in their voices;
Krystal has a dry, scratchy sound. Christina actually has two- her innocent teenage interview voice, and her liquid smooth mature singing voice. Neither are hard on the ears like Krystal's.
Conclusion: Christina is sexier.