I can understand how this is a difficult decision and there are pros and cons to both options.
A semester abroad would give you a good taster of the country and you're not committed to a whole year if it's not what you expected. It also means that you don't have an extra year of uni so can then go and work abroad or do whatever you want to do after uni sooner. However, you then have to live in halls for the rest of second year, and it might feel like quite a big effort to move just for one semester.
A year abroad would give you a really good immersive experience in the country, and allows you to spend more time getting involved with things there. And as you say it means you can live in a house for second year. However, it does extend your uni experience and so you have to be comfortable with having another year in education, and perhaps returning to uni for final year with different people. You also have to be more sure of your decision to go abroad for the year.
It would be really great to try to speak to people who have done a semester and some who have done a year abroad- maybe your uni can put you in contact with some, unless anyone on here has personal experience of either! I'm sure whatever decision you make will be right though and you'll have a great time