The USFL & the XFL (which starts next year) split the country. USFL is all east coast centric. XFL is the western US and actually has ties to the NFL to collaborate on rules, equipment, etc. The USFL from what I can see is basically a glorified college game, i.e. semi-pro league.
Because of the NFL ties, I expect the XFL to be more in line as an NFL minor league. I think teams will mine the XFL in the same way that some teams comb the CFL. Because the rules and style of play are going to mimic the NFL, what the scouts see will translate better. As that aspect becomes more apparent, I think the better undrafted talent will migrate to the XFL seeing it as a better way to showcase their talent. Because of that aspect, I expect the XFL to have better longevity. It's a model that will allow the league to set up in Europe and perhaps Australia or Mexico and be the NFL's international minor league.