"I really enjoyed talking and texting with you. You're a very outgoing, intelligent, fun guy/girl. However, I had a date with someone I really connect with and I'd like to focus on getting to know him/her better. I wish you only the best!"
Asking for a date instead of just texting shows real interest. You gotta take the plunge.
The guy who "won" was also more personal in his approach. We talked about things that matter, not just small talk. I met 4 guys online in 24 hours and was texting with all and had spoken to 3 on the phone. This has never happened to me before and so I really had to think about how I was going to handle it and sift through the possibilities. I also wanted to be fair to everyone and decide as quickly as possible. It was one week.