Here's a quick rundown
First off Starwood's hotels are generally far superior to Hilton's.
A Starwood hotel that costs 10K or 12K Starpoints would go for 40K-50K Hilton.
Starwood also offers Cash and Points, so for example for a category 4 hotel you can pay just 4,000 points and $60 instead of 10,000 points. Cash & Points often offers a great value.
Plus Starpoints transfer to dozens of airlines at favorable ratios.
20,000 SPG=25,000 US
20,000 SPG=25,000 AA
20,000 SPG=50,000 LAN
etc.
While HH does not.
20,000 Hilton=1,700 US
20,000 Hilton=3,000 AA
25,000 Hilton=6,500 LAN
Plus Starwood has other redemption perks like if you redeem points for 5 nights the 5th night is free and nights & flights where you can save even more.
Frankly there's just no comparison. Gotta love that uneducated AMEX reps tell people Hilton is better because you get more points for signing up.