Perennial link to a research article
the link should be valid as long as possible


There is no guarantee that Google Scholar will even still exist as a service in a few years, let alone that its URL scheme will stay the same. Who knows when another round of spring cleaning might come?

From the point of view of avoiding link rot, using a DOI resolver seems much better, e.g. http://dx.doi.org/10.1007/978-3-540-24775-3_5

Related: DOI® System and Persistent URLs


  Is there any DOI resolver that points to multiple sources, including free ones when available?


Citeseer does this, e.g. http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1.3819 - but unlike http://doi.org they have made no commitment to maintain this service in perpetuity. And they don't seem to be using standard DOIs, but their own internal ones.