Depends how you want to play...
Haywire blaster is cheapest, has the longest range and glances all AVs 87% of the time, making it the most reliable for stripping hull points. Not particularly effective against heavy infantry though, if you want to re-role.
Heat Lance is a bit more expensive, and outside melta range it glances AV10 on a 4 and AV12+ on 6s. If you take the risk of getting close you will start penning everything most of the time and get that bonus on the damage table to try to finish them off. The AP also gives us something that will threaten terminators, and that can be done at max range.
A blaster is more expensive again, shorter range (but not as short as melta range), but the higher strength will give you a better chance of penning outside melta range. Again, effective against heavy infantry (but you have to get *so* close!) and better against high toughness.