I have another Markevitch recording - the first ever to leave me with a favourable impression of this piece.

Symphonie fantastique by Berlioz
Berliner Philharmoniker
This in my mind is the better of the two Markevichs. The orchestra plays magnificently, unlike the shoddy ensemble coordination and intonation of the Lamoureux. I'm all for French sound, but the Lamoureux just play inadequately. The Markevich BPO recording, by contrast, produces some of the most magical atmospheres of all. The moment right before the idée fixe appears in un Bal is pure magic. It sounds as if a stunningly beautiful woman just entered the room and all heads turned in her direction and there was a moment of hushed silence. Nobody does this better. This recording is a real gem.
That Jansons recording with the BPO - is it available on CD?
No, but Jansons made an equally fantastic recording of the work with the Concertgebouw for EMI which has been reissued very cheaply. The interpretation is virtually identical and to me the Concertgebouw plays a notch better in that performance. But for one odd idiosyncracy (crescendos on the trombone fanfares in Marche au supplice that are not in the score - Jansons does it on both recordings and also did it when I heard him conduct this live with NYPO), the Jansons/Concertgebouw is to me one of the very best modern sound recordings of the work.
Beecham's FNRO is as close to a period instrument band as you are ever, now, likely to get as they were still in possession of that unique French sound (the horns vibrato the obvious indicator) and the discipline to match.
Sure, but why not take Cluytens with the Conservatoire orchestra who accomplishes the same French authenticity but is emotionally so much more compelling and coaxes far better playing out of his orchestra than Beecham, and the Cluytens is live!
Paray is different altogether. He moulded his brilliant Detroit band into the French orchestra of his dreams. Not for repeated listening but worth the occasional airing.
Except for the brass which have the unmistakeable not very French timbre of an American military marching band. They obliterate everything in their path in the last two movements. Sorry, I just can't warm to this recording. I also find Paray rather races through the first few movements. Of French conductors with non-French orchestras I would rather take Cluytens's protegé Prêtre conducting the Vienna Symphony on Teldec (early 90s) in the most stunningly virtuosic performance I have ever heard.