I own both the UBS text and the Nestle Aland text. As noted by the previous reviewer, there are some differences in how the UBS text notes variant readings. I find the UBS method to be both more complete and easier to read. (See below on the commentary available). I also find the text to be easier to read (slightly larger print, and I think the style of print is easier to read too).
A point of clarification, though, regarding the basic Greek Text. My understanding is that there is very little if any difference IN THE GREEK TEXT between these two editions. They BOTH rely and build upon the work of Wescott and Hort in textual criticism, and reach very similar conclusions about the "best readings" for any given variant.
The companion volume (A Textual Commentary) also published by UBS is a GREAT addition. It helps you understand why the committee reached the conclusions they did about which reading may be the best reading. Note; whenever a variant reading exists in the extensive library of ancient manuscripts, it is noted in the footnotes (Critical Apparatus). There is also a note as to how comfortable the committee was about their selection of the best text. An "A" rating means that there is no question in their minds. A "D" rating might mean that the selected reading is only very slightly more likely to be the original reading than one of the other variants. (I hope that is clear). In some cases I have taken exception with their decision on "D" readings, and it helps to know that they were not completely comfortable with the choice they had made.
One advantage of the Nestle text is that it is just slightly smaller and easier to carry (a vest pocket edition. (As noted above, you pay for the size in it being not as easy to read.) My copy of Nestle is cloth bound while the UBS text is bound in vinyl/plastic. My UBS text has proven to be very durable. A word of caution... don't leave it on the dashboard or seat of your car on a hot day. The heat WILL damage the binding.