i agree with adinu and cstradling. if there was one "best" dell laptop for students on a student budget, wouldn't you see almsot everyone with that same one? because we don't see that (or at least i don't, and where i go, it seems like there is about 1 laptop per person) i doubt there is a best. if you broaden it to "most common", i'd say the inspiron 15.4" and 17" models (both the older and newer) would be up there, as they are more suited for the generic person, or can be customized suitably for most users, and can generally be cheaper. some might get the latitudes if they want it a bit more durable or buy it through the school (i.e. discount) or just like the "professional" look a bit more. gamers will lean towards the XPS line (typically). and some engineering will go for the precisions, but that is less common, though I have one, and i'm in engineering, and at this stage, it really doesn't make all that much of a difference in terms of the software i use and the level of the work i have to do with it. it all really boils down to whether the user is going to be using it a lot (maybe will spend a bit more on it), transporting it a lot (buy a more durable one, or a smaller one), using it as a DTR, gaming, etc. basically, there is no "best" but more often a "typical."
also, since the laptop models change every year or so, it's hard to have a "best" or "fills the needs" because i would argue that for a lot of students, a pentium M 1.6ghz in a 15.4" wxga is good enough, and that could have been had in a inspiron 6000 almost 2 years ago.