Hi RTID
Good to hear you're on the bike!
With a 105 groupset, you have good mechanics irrespective of which brand you go with. Really, outside of the groupset, it's really down to what feels (and looks!) right for ya.
I've a Giant and a Planet X road bike. Recently bought the carbon Planet X on line from the UK. A mix of Ultegra and 105 groupset. Typically for me, issues with the rear dérailleur and now I've got to deal with overseas to get the issue sorted. So, as you are UK-based, perhaps deal locally in case you do run into a rare issue like I have. :-(
Good luck with it!