I wouldn't say there's one thats better than the other it really just depends on the build of your army. I only use healers in MP and don't take any healing (Unless I use troop card that has healer in it) to war as I choose to add more offensive power which works well for me.
Supply vehicles positives - Less troop space, no oil loss, receive bonuses from museum/barracks (Barracks -Assuming you are CWA), healing amount can be raised up museum. Negatives - Low HP, basehealing amount is lower which is why they take less troop space, can be debuffed by museum though to be realistic no one is going to carry that armor piece and even if they do you can't see affect.
Tac Helo postives - More HP, my fav is the ability to drop troops (I don't loot oil only I always go for 100% which is stupid I know) so I keep wall breaker and when I need get into a spot I drop the wall breaker inside and he destroys the wall to get out. Sometimes dropping from the outside going in isn't a great idea depending on the defense. Negatives - Uses Oil, costs oil for factory and armory upgrades, troop space count, receives no bonuses from museum or anywhere for that matter.
Clearly they both have crappy AI so I don't want to list that twice. The supply vehicles can be easily killed by a bad rally as they may run the long way around if there is an opening. The good thing is that if there's no opening the supply vehicles will stay behind your army. That can happen on a maze base. Tac helis have the same problem which is that they are too direct. Because they can fly over everything, rallying anywhere on a spot will cause them to fly there (Good for raids but not so good for fights) so they may be the first to die. There are cases to be made for both you just have to try them though tac helis do require much more of an investment just to try them out. But again this debate is more for MP than for war as most higher level players and more seasoned attackers will not take a healers in order to add more offensive power to cut down attack times. I'm sure I missed some stuff but those are just the things I notice.