Wow, what a choice! Those that have been mentioned above are all great. But I guess I'd have to choose LAND OF THE PHARAOHS. The score is part of what makes that film so much fun to watch.
My first thought would be THE FALL OF THE ROMAN EMPIRE. I have had the LP since the '60s and picked up every improved and expanded release. So it's been my fave for a while. It wasn't until a couple of decades later when an full version of LAND OF THE PHAROAHS came out that I switched my allegiance to that score. What a treat. It's beco0me the epitome of glorious Tiomkin excess to me ever since. I'm pretty sure it's not what ancient Egyptian music sounds like, but it oughta be.
For me - impossible. The following 4 scores are all on equal, glorious footing:
1. The Alamo 2. The Fall of the Roman Empire 3. The Guns of Navarone 4. 55 Days at Peking
But if I had to take only one with me to the desert island it would be 'The Alamo'. It was the first soundtrack album I ever obtained (in 1961 for my 10th birthday).
Something which has always astounded me about these four is that they are so vast in their scope and ambition and were written one after the other when Tiomkin was well past 60 years old!