Sure thing! I am currently attending UW's program. The major factor for me was the studio cohort model of MHCID and the focus on design alongside HCI. I think it will give me more flexibility coming out to go into tech/traditional HCI or go the design agency route. Seattle was also a huge factor for me just in terms of jobs (I love London and Seattle both as cities, so not as much as a livability thing). All the major tech companies are here and the MHCID program also has a lot of connections to SF if I wanted to move down there. The capstone sponsors for MHCID are incredible (NASA, Google, REI, Microsoft etc...) which you just can't get outside of Seattle or California.
All that being said, UCL is a great school and I'm sure I would have really enjoyed it as well! Feel free to message me if you have other questions.