I'd say the Westin is a little better for room/hotel quality, but the 4P has free wifi in the rooms ($ at the Westin) and much better street parking ($ at the Westin to park on-site), plus a hotel bar with over 100 kinds of beer (the Westin's bar is a generic hotel bar), which usually clinches the deal for me. If none of those matter to you, then take the Westin.

That being said, I wouldn't spend 3000/4000 points on a free room at either if I could find a room for under $100 at LAX (which you can often do), unless I was flat broke and this was the only way I could pay for my room. LAX is stuffed full of cheap 3-4 star hotel rooms on Priceline/Hotwire, or off of the hotel sites themselves- (I've gotten places like the 4P, Hilton and Renaissance Montura for $80 all-in or less that way- no stay or points credit, but a perfectly fine price for an overnight stay at a decent hotel). 4000 points + $60 can get you a Category 4 on a Cash and Points award, which is very often a much higher use of your points- that can save you a couple hundred dollars off of the cost of a room if you do it right. For instance, I've burned points+cash to stay at the Sheraton Delfina in Santa Monica. Rooms were running well over $200 for the date I was there (Grammy weekend). I paid $60 and 4,000 points.