Off the top of my head I can't think of anyone I knew from law school who applied for federal appellate clerkships and struck out. I certainly know many, many who weren't on LR and probably didn't have top grades who landed awesome federal appellate clerkships though of course grades and LR don't hurt. The big deal is which judges you can get offers from - there's a huge range in competitiveness from one individual judge to the next (and between circuits as well).
My point was that you're not guaranteed to get a clerkship from any school. The clerkship hiring process is extremely random. Although you can bolster your chances by going to top schools, getting top grades, and knowing the right people; once you've met those criteria, the clerkship hiring process is largely out of your hands. This question is similar to the "how do I get to WLRK" question. Going to the best schools, getting top grades, clerking for a prestigious COA or SCOTUS, and knowing the right people will help, but ultimately, it's a crapshoot, and you shouldn't go to one particular school just because you might have a slight advantage of landing WLRK from that school. Similarly, once you get into those top schools, there is no set school that might give you a significant competitive advantage over another in terms of clerkship placement (at least, not so significant as to make a choice of school based on clerkship placement alone). I personally know several people in the T14 that were at the top of their class, on Law Review, and still struck out on clerkships this past year. Once again, I warn the OP not to select his school based on where he might have the best shot at a clerkship.
On a side note, I really am excited that all of your friends applied for, and received, federal appellate clerkships from HLS, however, I'm not certain that your anecdotal evidence disproves anything that I've written - especially since people don't tend to disclose the fact that they failed to get a clerkship or job to people that they don't know (or, even to their own friends, for that matter). While we're throwing around anecdotes, let me add this: I personally know of HUNDREDS of HLS grads that have been passed over for clerkships in my Judge's chambers. I also know that some of those same
applicants called our chambers the next year to inquire as to whether the position was open. It, therefore, seems doubtful to me that EVERYONE who applied for a clerkship at HLS got one.