What do you want?
1) Rapid knockdown?
or
2) Security against reignition?
For (1) you have Dry powder, either a high MAP content ABC or if you want serious power BC's such as Purple K or Monnex, all in 9 kg (8 for Monnex). The highest rating you can now get under EN3 is 233B, meaning that the advantage of these agents isn't a seasily apparent (under BS5423 they would have been 296B).
Of course you risk re-ignition or flash back and if there is equipment that could shield easy access to any pooled liquid you could end up chasing the fire around in circles until your extinguisher runs out (unless you work in a pair). Practical training experience would preferred (and not on a basic LPG rig) - if you want to see why then look on Youtube at some US motor racing footage - in one good clip a mere 20-odd litres of methanol on fire defied the attempts of the (poorly trained) crash crew despite using four 5 & 10lb, three 20lb & one 150lb skid mount powder & a 10lb CO2 extinguisher.
For (2) you want the good old Foam branchpipe extinguisher with AFFF-AR or better FFFP-AR. You can extinguish in stages, don't have the 'all or nothing' problem of powder and good security against reignition. Of course it's slower, you may need more of them (remember the old 5306-3 Class B calculations with foam being grouped in three's?) and if you're fire is flowing you are in trouble.
In essence there's no one 'best' answer - each has it's pro's & con's. The nearest to best is dual agent, with Powder for initial knock-down, followed by foam for security as used in the UK Motorsport field (the 2x4 approach, or is it 4x2, can't remember which way round at this time of night!)
Your typical extinguisher company would just bung a 6 kg ABC in of whatever flavour they are selling at the time & leave them to it - in which case, 'get out-get the fire brigade out-stay out' is best.
Turning things on their head they could have a policy of immediate evacuation for all spill fires and just have a CO2 in case it's just the equipment or control boards going up.
You don't hear much about the Foam-master these days - invented over 30 years ago by Pyrene/Chubb, initially only on low expansion, but the recent equivalent also exists with a MX branch. Available with fittings for buliding or vehicle small bore hose reels it hold enough FP, AFFF or AFFF-AR to give it the same amount of finished foam as 20 nine litre Foam Branchpipe extinguishers - aimed more to industries (or small airfields) with a formal fire team or brigade.
