General rule of thumb: the bigger the reflector, the more light.
If you're on a 250$ budget, its hard to beat a tried and trued technology as far as lights go: Aircraft landing lights. There are several 13 volt sealed beams available, and for the price its hard to beat. The PAR36 (4.5") and PAR46 (5.75") bulbs are readily available at your nearest NAPA or farm supply store, or even cheaper from rock auto. I ran 2 GE 4509 100w 4.5" spots on the front of Toyota for years tied into the high beams with a relay, and for the price at ~30$ a light, they were damn hard to beat. You can get flood bulbs too that fit the same rubber housing. NAPA part number 80374 are the 100w spots WITH the housing, and are 24$ each. I'm running dual filament GE 4700's in the bottom grill of my mustang, with one filament for spot and one for flood, both running when I hit the switch. I've since upgraded to Hella Ralleye 4000's, but for a true budget light, the old sealed beams are hard to beat. The rated life is only like 25 hours, but thats also in a sealed housing with no airflow. I've got at least 40 hours on the set I pulled off the truck and they were working when I took them off.
To answer your original question on the square vs round debate: square housings do tend to limit the output, both in width and height, due to the limitations of not having as much curvature for the light to reflect off of.
For roof or cab mounted lights, try to stick with spot beams as they won't tire your eyes by reflecting off of the hood.
I've had (and currently have My Big A** Hella 4000's) hid swapped, and while they are brighter than halogen, they tend to lose their beam pattern, resulting in less light where you want it.
Although the newer LED's are pretty nice for up close.