Perhaps I should clarify my stance:
Both games have flaws. Xenoblade has numerous flaws, but small ones, and mostly outside of the main story (character models, sidequests, difficulty, equipment, menus, tutorial overload etc.), whilst TLS has fewer flaws, but much bigger ones (lack of variety, less than 20 hours long, dull story, uninteresting battle system, lack of freedom).
Both games have advantages. For example, Xenoblade's world is amazing, whilst TLS has a great city. Both have great VA, but TLS' soundtrack is a tad meh. However, TLS' dialogue is genuinly funny, especially Syrenne. Both games have some great sidequests, but TLS has too few, whilst 70% of Xenoblade's are a bit meh.
Both are great games. But TLS' flaws are just too big for me to consider it a contender to Xenoblade. I can forgive Xenoblade's flaws, because of what it does right, it does REALLY right. I suppose it's the same with TLS, but it felt more like a demo to me. Hopefully the Mistwalker and Monolith WiiU projects will capitalise on their strengths and produce even better games.
The choice is yours. If you can forgive Xenoblade numerous small flaws and get over its slow, overwhelming beginning, you'll find, potentially, the roots of one of the greatest JRPG's ever made. However, if you can't, then TLS gives you the better introduction, so long as you can cope with it being short and restricted.
...why didn't I say that in the first place?