I'd go with the HPS as it is the tried and true standard.
As far as heat goes, 250 watts of electric is 250 watts and the heat should be about the same whether it is HPS, MH, INCANDESCENT OR CFL.
Everyone gets worried about HID bulbs because they are bright, at the same time wouldn't have a care in the world over putting (4) 100 watt incandescent bulbs in the same place and that would be putting out more heat than a 250 watt HPS.
Just run some fans and hang a thermometer, you'll be amazed how cool everything stays if you have air circulation.