Vinh- Cash flow is important to me strictly based off of the home, area, note and game plan for that property. -$300/month is not something I would be interested in unless the tax savings is fantastic on it, making up the difference.
I have a property right now that rent vs expense is about even, however, I receive some tax benefit because of it and it will be paid off in 8 years. (originally a 15 year note). The house and neighborhood are nice and I have minimal concerns about a drastic decline.
I'm a conservative investor, the 30 year note appeals to me in 1 way. You have more buffer in a down turn. If/When the market corrects, how is that going to adjust rent? If rent decreases, how much more negative will the property be? No one knows, but can you afford it? Are you in an industry that could be affected by a down turn? If you don't have big cash reserves and could not afford any more negative cash flow, you may want to consider parting ways with the property...