Re: the six times bonus - it took about 2 months for it to post on my account after a couple of emails to/from both US and United.

The 2nd time I took the US Shuttle for the bonus, it posted in about a week, so Im not sure what went wrong the first time.

Parking - I like the parking lot better for US rather than Delta. Delta has 2 lots - the closest one is always full, and IM forced to use the farther away one, which is a long walk if the parking bus is not there.
The US lot is across from the terminal, and Ive never had a problem finding a spot.
And since Im not coming from Manhattan, I like the fact that the US shuttle is closer to the beginning of LGA rather than the end of LGA.