Access wise, you'll stuck like the Westin Ebisu, getting their from Narita Airport via train would be a pain if you had much luggage, as it would require about 2 transfers. Its near a subway station the Mita/Nanboku line that you can go onto connect to other lines of the Tokyo Subway or connect to JR lines or other rail lines at various points.

I don't know all to much about the Miyako Tokyo and I don't know what type of "renovations" they are doing, but the standard rooms in the Miakyo Osaka are your standard japanese business rooms (though a little larger in size) with dated decor, which appears to be the norm in Japan if you're paying for the cheapest rooms (and standard award rooms), I never had a problem, since I often stay in business hotels anyway, and I'm not that picky, but others might give it a different view.

The higher club, premiere etc rooms appear to be more modern. Access to the Osaka Miyako is on the Kintetsu Line a little east of Nanba in Osaka, guess it all depends on where you plan to stay and visit, Nara can be reach easily from the Kintestu line in Osaka as well.
Alternately, the Westin Osaka is located in the North in the Umeda area.