So, apparently, there is this brewing controversy about which is the better recording of the Eroica by Klemperer, between this mono recording of 1955 and his better known stereo remake from 1959 (Symphony 3 or The Klemperer Legacy: Beethoven Symphony No.3 ("Eroica"); Grosse Fuge). Let me enter the fray, then; my title states clearly whose side I am championing.
The pro-1955 have given here the reasons of their preference, I'll develop the reasons to prefer the 1959 remake. Sorry for the seemingly dry stats, they are just to give an objective basis to subjective impressions.
First, at least in the first and third movements, the basic conception of both versions is remarkably the same. It is almost to the second in the scherzo; the first movement in 1955 is overall swifter by some 45 seconds, but still, the opening pulse is almost the same: in 1959 Klemperer crosses the repeat bar at 3:34, against 3:28 in 1955 - not a dramatic difference, then.
What both versions have in that first movement is a very characteristic sway, a gently rocking beat that is established by the deliberate pace and remains under the music's explosions. But that Klemperer in 1955, while establishing the same basic pulse, should finish ahead of Klemperer in 1959, points to the fact that there is indeed an added bite and urgency in 1955, perceptible from the begining but even more pronounced as the movement unfolds; Klemperer in 1959 remains remarkably stable and deliberate in his beat. Klemperer's accents in 1955 are also slightly more biting and explosive; they are heavier in 1959, but also sometimes more powerful. Still, these differences aren't enough to make up for the deficiencies of the 1955 sonics: the mono recording is distant and unidimensional, robbing the music of much of its power and impact. The kind of massive and powerful approach that Klemperer sets forth needs the spacious and vivid stereo sound that he gets in 1959 to convey its full impact; in 1955 it is more a case of having to imagine that impact, rather than actually feeling and experiencing it. The 1959 stereo also lets you fully enjoy the antiphonal placement and dialogues of first and second violins. In the scherzo (which, I find, at its easy-going trot, lacks in both cases the kind of bubbling energy conveyed by the brisker approach of Toscanini and the likes, although, heard "on its own" rather than comparatively, it makes its effect), thanks again in part to the vivid sonics, there is much more instrumental character, in particular with the horns in the central trio: 1955 is like a black and white photocopy.
The interpretive differences are more pronounced in the two other movements. The finale is slighly but perceptibly more urgent in 1955 (in 1959 Klemperer's stateliness here oversteps the limit that turns it into plodding). All things are relative, of course: the urgency of the 1955 finale still doesn't make it a very urgent finale. But it is really in the Marcia Funèbre that the two versions stand out markedly. In 1959 Klemperer is slow, funeral indeed, more a lament on the plights of mankind than a true march, or if a march one with a huge cross on the shoulders: 16:47 of trudging to the Golgotha. This is the kind of approach already illustrated by Furwängler (17:16 in 1952 with the Vienna Philharmonic, Symphonies 1 & 3), and later (in 1963) by Karajan (17:02, Symphonies 1 & 3). In 1955 Klemperer is considerably swifter: 14:36; Klemperer fans may be surprised to know that this is faster than Toscanini (who, contrary to his reputation, is far from fast in the Funeral march; I have his 1949 recording, Symphony 1 & 3). In fact, and by way of paradox for the "slow" Klemperer, this swiftness places him into the opposite extreme: Toscanini, Munch, Walter, Bernstein, Szell are all between 15 and 15:30 and lump into a "mainstream". At 13:18 Scherchen is the speedy rabbit (and the closest to Beethoven's jaw-dropping metronome mark, Beethoven: Symphonies Nos. 3 & 6) but, among the versions from the 1950s and 1960s, I've heard only Leibowitz who takes it, like Klemperer, under 15 (Symphonies No. 1 & 3).
Preference for either of Klemperer's Marcia Funebre is a matter of taste, of course. But far all the vehemence that the greater urgency allows for, my point here is: what is the point of a "swift" Klemperer? For "swift" we have Scherchen and Leibowitz and Toscanini, that was their trademark (to say nothing of the Historically-informed performers of today). What makes Klemperer, and Klemperer's Beethoven, so unique among a zillion others, is that he is slow, deliberate, massive and ponderous. Indeed, his 1959 Marcia has a unique eloquence. Add to that that, again, the great 1959 sonics lend it an instrumental character that the 1955 version can't even start to emulate. Just try at 9:11, when the horn erupts: it is grandiose. 1955 by comparison is anonymous here.
There are many excellent to outstanding versions of the Eroica, and, from Furtwängler to Scherchen, many and widely differentiated options to choose from. What makes Klemperer unique is that very deliberation and massiveness that some amateurs seem to take exception with. For all its additional bite and urgency, and partly because of its indifferent sonics, I find the 1955 version ultimately rather anonymous. The unique character, the "authentic" Klemperer is in 1959.
But, to cap it all, let me put everybody in agreement, the advocates of 1955 and the champions of 1959: in our enchanted kingdom of music, the best of both worlds exists. It is called "Barbirolli". Barbirolli recorded the Eroica in 1967 for HMV and it's been reissued by Dutton (Symphony 3 / Elizabethean Suite). Now THAT is truly one of the great recordings of the past century. It has the deliberation and massiveness of both Klemperers. It has fine stereo sonics, maybe not as outstanding as Klemp' 59, but that's something you will hear only on close comparison. It has none of the stodginess of Klemp' 59 and all the bite and muscle of Klemp' 55. It has the brisk and ebullient scherzo of Toscanini. Last but not least, it has the slowest Marcia Funebre I've ever encountered - 18:10 - and the effect is extraordinary: Atlas bearing the burdens of mankind on his shoulders. This is the version of "the Eroica by Klemperer" that the amateurs of Klemperer need to have in their collection.