I have a hard time putting 3 over 1 based on replay value alone. Yeah, 3 is more epic, better quality graphics, set pieces, etc... But UC1 is just a more fun game to play. I beat 3 once when I had a bootleg copy on my jailbreak PS3. I got to the end, but never finished it once I bought it for my official PS3. I bought the collection and beat 1 and 2 mad fast. But I've already quit 3 and lost interest in playing it. I've probably beaten UC1 like 12 times at least though.
I personally found UC3 weak. I put UC3>>>1 because I know a lot of people aren't really into the series like that and will only remember the set pieces and not the actual game around it. UC1 is dated sure, but it was a fun little game that kicked off the series. Just a few characters, cool little action scenes, funny and great writing and it wasn't too long.
UC3 tried to 1up UC2 by creating even crazier set pieces but due to it's rushed development, it was weak in the long run. I beat UC1 twice and UC2 like 5 times including the remaster. UC3 I only beat once and I struggled to play it on the remaster. This one though I may beat one more time since it's a pretty long game and not something I can run through randomly.