Depends on what you need.
If you want a quick source of steam power, go LP Boilers. They don't take much to bring up to fully operational status and it provides a good amount of power for the amount of work you put into creating it.
If you're planning to go all-out insane and supply substantial amounts of both Buildcraft MJs and IC2 EU, then you definitely want to start an HP Boiler. LP Boilers are nice and all, but they just fall short when you want to squeeze out as much steam possible. Just be warned that HP Boilers take forever to get to full power and you'll need an insane amount of fuel.
At the moment, I use an HP Boiler to run 5 Industrial Steam Engines to keep all my Buildcraft goodies juiced up, and a Steam Turbine providing power to two MFSUs. One is dedicated to UUM production, the other is for the chargepad and manual processing. Trying to run that with an LP Boiler just didn't cut it, and adding 2 more Industrial Steam Engines would start emptying the steam out of the boiler.
But that was back when Tesseracts didn't exist and I had to manually charge and swap Energy Cells for my Quarry. That just drained lots of power out of my Buildcraft power supply.
From what you're doing though, an LP Boiler should work just fine.