They work well togather!
Recently, I've seen many commanders begin to press for longer and more drawn out games, as free upgrades help to destroy the marine early game advantage it seems comms are looking more for the top-teir tech against Hive-2 victory. Now, this is largely based on res nodes in many cases as to who is the victor, however, I have seen a number of heavy trains be wiped out by a single stomping onos with support, or waves of jetpackers slaughtered by carefully placed OCs and skilled lerks and fades.
My main point in this topic? Jetpackers and Heavies work wonders when used to augment one another. Say a team of 3 HA HMGs, 1 HA GL, and 2 JP HMGs and 1 JP Shotty or GL if you have a player left over; all have welders. These players can save each other from a horrid doom. Jetpackers can target onos and bring them down FAST even with stomp; especially if you have that 3rd JP. Obviously the numbers of these groups should vary depending on the makeup of your oppononet; more onos should cause you to drop more JPs to avoid the deadly stomp of death. A lot of lerk gas or Fades or OCs should lead to more HA's. Remember, even JPs can massively benefit from welders, especially if you have armor 3 which you *should* have unless you're doing some sort of nutty rush strat. : )
A group of HA's with a couple of JPs playing anti-onos support is infinately harder to kill, plus the JPs can always get good vantage points to cover when HA's are having trouble; or they can just play rear guard well by being able to move backwards quickly. On the other hand, HA's provide the punch and damage taking abilities that JP's lack, while also providing the immunity to gas which is crucial against a large-lerk alien team.
My *other* point I'm going to leave you with here is: Always remember to alter your strategies as the situation changes! In time the aliens will find counters against virtually any strat, so remember to cover your weaknesses and change your strengths as your enemy shifts too. The ability to adapt to your enemies weaknesses will *ALWAYS* beat a static strategy.