For me, Mozart's "Requiem" is the Cinderella of the recording catalogue: a myriad versions yet hardly a one that is really satisfying. I'll put my cards on the table and say I am not enamoured of HIP, period instrument versions with thin tone and under-powered soloists; I like a bit of heft and grandeur to a Requiem almost as beseeching and fear-struck as Verdi's. I do not respond to Gardiner's rushed, perky and shallow account, nor Corboz's bland, nondescript effort with indifferent soloists, nor Böhm's interminable ponderousness. Too many versions are flawed by the choice of singers (for instance, I cannot live with the one by Franz Worse-than-Most, who also sounds as if he has a train to catch). Barenboim, like Böhm, is infected by lethargy, and both Gedda and D-F-D are having a real off-day; even Janet Baker and Sheila Armstrong can't revive that one. The later Barenboim has some poor singing, too. There is Bernstein, but it finds him at his most self-indulgent: too mannered and too slow - and his soloists are weak. Davis's first recording is afflicted by a groaning bass and a tenor who sounds as if he needs to clear his throat; his second is better but bland. Both Marriner's weedy account and Giulini's self-conscious version are ruined by Robert Tear's bleating, and as for Norrington - don't even go there...
I like the three Karajan recordings more than most - the usual complaint of his being too "slick" and "polished" and for many Werner Krenn's nasality is less than ideal in the most celebrated version from 1975. Abbado, excellent musically with good soloists, seems to have been recorded in a barn (OK; a cathedral - same effect) with far too much echo. I haven't yet heard Harnoncourt, which looks interesting. The live Solti with the VPO is a distinct runner: Solti became a great Mozart interpreter in his latter years and this one is special in that it's a live Mass with the liturgy in German, the text interspersing the music - but for that very reason it might not be the recording to live with.
So I've on and off been seeking a "perfect" recording for years and have kept returning to one old favourite: this remastered CfP issue of a 1968 recording by De Burgos with excellent soloists. Some find him a tad sluggish, but I think he finds real nobility in the music and there is great pace and drive in his "Dies Irae"; no hanging about. George Shirley's grainy, plaintive tenor may be an acquired taste but I love his intensity and he is ably partnered by some real star singers in top form - surprisingly, perhaps most impressive is the relatively lesser known Marius Rinztler, whose resonant bass brings power and authority to "Tuba mirum" The orchestra and chorus of the New Philharmonia are simply terrific.
So until the paradigm of recordings appears, this is my default choice - and you could do a lot worse (see above...).