I have handled both (Sterling vs LV) and for the small price difference, one should definitely go for the Sterling square, because its narrow blade is narrower and longer than LV's which can be critical for very narrow dovetail work.
The much more expensive Vesper square, like planes costing $3,000 a piece, won't make you a better woodworker or your work finer. But it is a boutique tool and it is to be had not just for functional reasons and hence shouldn't be judged on that count alone. I have seen woodworkers with fancy and expensive marking tools and their work; suffice to say that the two have no cause & effect relationships (and that applies to most other hand tools).
Simon