the quality is the same as your cable that you use to connect the device to the tv. If both boxes use HDMI then both output using the HDMI. The difference comes from the network themselves whether they are broadcasting in 480p, 720p, 1080i, or 1080p that will depend on the network your watching (example abc, espn, hbo, showtime, amc ... etc) as they control what video output is broadcasted per their channel and/or per whats being broadcasted at that time. Another difference is your TV in what type of output it can take. Just cause you have an HDMI cable and the device such as tivo outputs in 1080p doesnt mean your tv does. If your TV only goes up to 720p then that's the max you'll get out of it no matter what you do or which box you have it's all or nothing type of scenario.

best bet is to call tivo and ask that question. normally a fee is involved in any dvr of any company you choose as their is a fee. tivo only has one fee for service as others have rental fee hd access fee surcharges and the fee can change over time such as price increases and so forth when tivos fee remains the same as long as the plan or box is active