Everyone's situation is unique. But facts are facts. Good regionals have come and gone. US has stuck around. It hasn't been a great place to work for some, especially late-90's hires, but it has hung on and is in position to be a GREAT place to work.
Regionals work for some, but for the most part, all of the reasons I heard NOT to go from a regional to US have turned out to be falsehoods.
The old saying, the worst day at a major is better than the best day at a regional, has held true for me. But like I said, everyone's situation is different. I myself was so tire of 4-day trips and 95 hour lines, so my live-in-base reserve life, flying about 20-30 hours a month with very few overnights is a welcome respite!
To each his own, but my personal advice is to save your money while at a regional so you can afford to make the jump. Apply, interview, then decide yes or no once you have the offer. Until then, it's not up to you!