I'm not sure why anyone would use the RRSP first time home buyer plan. 5 year mortgages are in the low 3% range. Investments should be more then that. I suppose it could work out tax wise to do RRSP's to get the lower income tax then get your tax return and pull from the RRSP to get the downpayment.
The HBP lets you basically leverage funds earmarked for retirement for something more useful now, rather than 30 years from now. Before this was a great way to have assets grow tax-free to get the equity needed to get a down payment. It was even accented since some workplaces would basically double your contributions, which can work out very well at creating some assets. However, with the TFSAs now, the HBP is, imho, a poor choice to use (there are some cases it is great). In most cases you basically use it to borrow against your future self. Because most people start at the bottom of the pay scale when they buy a house, and move up to a higher taxed bracket over time, the HBP actually costs you more. This is because repayment dollars are made with after tax, and since the marginal rates typically go up for a person over the 15 year repayment term, they end up paying more. Sadly it is just a way to get something now, rather than wait it out.