The Soma is a great looking minivelo, I guess it all depends on your budget and commitment. If, as you say, you are a newbie to the bike world, then the mercier will let you test if you actually like it or not for less money, and then if you do you will be able to upgrade as you wish.
If you are sure to like riding, Iīd go for the Soma. Itīs a great package, and thatīs a really good price.