I can't speak for the Avanti or Giant, but I ride the 2012 Metrix 20. The 2012/2014 Metrix frames appear to more or less the same, but my 2012 is equipped with Shimano MTB components (27 speed Deore and disc brakes), while the 2014 has road components (18 speed Sora, Textro brakes and carbon fork). Primarily due the disc brakes and alloy forks, the 2012 is about 24 pounds while the 2014 is spec'ed lighter at about 21 pounds. My understanding is that disc brakes disappeared with the 2013 models.
Having said that, for me, I love the ride on my Metrix 20. I use it for commuting to work in the summer (20kms round trip) and weekend fitness rides (50kms round trip). Being more upright with the flatbars works for me. The frame is very stable and responsive, and I find the setup is fast with a very wide gearing range. I just got back into cycing in 2013, since I have to step aside from team sports in the short term to recover from a torn rotator cuff injury I suffered playing ice hockey. I am 5' 7", 138lbs on the Small size frame, which fits me very well except I found I was cramped in comparison to my classic Bianchi road bike. I solved this by changing out the stock 90mm stem to a Uno 100mm ultralight stem. Also upgraded to, or in process of: Shimano XT SL-M770 shifters, Wellgo R025 pedals, Merek carbon seatpost, Prologo Nago Evo seat, Ergon GS-1 grips, and carbon handlebars. The upgrades are for a combination of improved performance and/or weight reduction. I prefer to go with traditional clips and straps on my pedals rather than clipless.
From a quick web look, the Avanti it is equipped with Alivio/mix MTB components while the Giant has Tiagra/mix road. Your 2014 Metrix has higher spec'ed derailleur and brake components, and your 50-34 crank is going to give you plenty of range. The frame is plenty good to do upgrades on whenever you are ready. I would start with the pedals - the stock low end Wellgo's are truly **** and you may want to go clipless. Your setup is reasonably light (lighter than mine by a few pounds, so I am jealous), and you will be going pretty fast if you want to. If you want to go faster without much cost, you can switch up the tires to 23/25mm. Whether you want to will depend on the quality of the roads you will be riding on. I find the stock 28mm Ultra Sport's to be very smooth and comfortable. Assuming that you do not have any buyer's regret with your choice of a flatbar versus drop handlebar setup, I think you are going to be very happy with the Metrix 20.
