One's ridiculous and over-the-top, the other tries to be more serious and grounded. Which of those you'd deem better would depend on personal taste lol.
Under Siege 2: Dark TerritoryThe first
Under Siege is unquestionably Seagal's best movie (some might argue it's his only genuinely decent movie). Sadly the sequel doesn't really live up go it. It's entertaining enough, but it really feels like it should/could have been better. Still, the head mercenary character's fun and Eric Bogosian is clearly having a ball as the villain. Also the finale is an absolutely spectacular slice of ridiculousness.
Spoiler
I especially like how the mercenary they get to drive the train once they've taken it over stays there until he kills himself ploughing headlong into an oncoming train. Did he sign on knowing he'd eventually commit train crash suicide? Or did they just leave him there and not tell him?