There is armor. Ten times more valuable than all the health around.
Although sadly, it is only in the beginning near the bank.

If I could insert my image here, I would.
I marked the bank and the armor both on a section of blank map.
http://i242.photobucket.com/albums/ff109/GTASynch/3_Leaf_Armor.jpg

To scope it out, take the LONG drive over there, pick up the brothers,
and head to the bank, but don't enter the mission marker.
Simply drive around the block. You'll see it laying in the street.

Now if you were to drive straight to the bank from Packie's,
you will notice it's on your left, outside of an alley.

This is where the bank escape begins.
Fire off a few rounds at cops, when the doors are open,
to get the brothers to head down the alley on the right.

Once they do, Packie says you are on crowd control.
At this point pick off a few FBI guys and then...
There is an alley to your LEFT. If you go up and around,
to the right there will be the armor in the street.
The downside, you are leaving Packie and Derrick in the alley.
The upside is, you get armor BEFORE the cop car parks on it.

Now go back to before you grabbed the armor, and look at this
downside. Coming out of the bank, down the alley, on crowd control,
you can pick off FBI guys with the M4 then RPG the cop car.
Unfortunately, running forward, straight ahead to alley end,
there is now the cop car parked on the armor down the street LEFT.
There is also a cop hiding behind the dumpster.
The best bet there since YOU WILL be following the guys in that
direction,
is to pick off the required cops left (Red Blips on HUD are required)
and then head to the armor/cop car/cop hiding behind dumpster.

Once cleared, they head for the alley where the NOOSE vans show up.
Take cover and use the wall to pick off required targets.
Following Packie and Derrick after this, stay in between them
for another fight.

Once you get to the cut scene with the chopper, a new brand of hell
awaits.
Trust me I've done this mission a number of times testing for things.
Even gone back after passing, to trace my steps....sorry, I'm an
explorer.

In the beginning of the subway pick off two cops then head down, and
take cover.
Don't rush in, it looks like there is only two, but a wave of NOOSE
guys is heading up the
stairs.If you really have the time which you don't, accurately toss a
grenade down the steps.

That worked once in 3 times for me, there are too many, and Packie and
Derrick
take them out. So stay covered BEFORE grabbing that health on the
wall. Once
the NOOSE guys are cleared coming from below, follow the brothers
after grabbing
the health on the wall. Once on the platform, 1 or 2 RPG's should take
out the guys
across the tracks.

Tricky, watch for trains! Once on the tracks, then get a healthy
distance and SNIPE
the NOOSE guys battling Packie and Derrick behind you.

More tricky....You then come to the service exit marker.

You can do a few things here:

1) Enter the marker, don't stop, run after grabbing wall health up the
stairs as fast as possible
and through the service rooms and out the netting to grab the first
car you see,
this has worked a number of times, lingering brings cops.

2) Avoiding the marker and trying to run down the tracks does not
work,
the wanted level circle follows you. Kids have reported this works on
my site,
I tried it, it doesn't F***ing work.
Maybe if they are ENTERING the yellow arrow, then run down the tracks,
you can ditch
the wanted level, but without entering, it is a waste of time.

3) Enter the marker, then run up, and the wanted level is reduced to 3
stars.
At this point many players have reported calling that one girlfriend
who
gets rid of the wanted level over the phone. This has been confirmed
to work.
I haven't tried it, but it makes sense as I have used Dwayne's backup
in story missions.

If you can lose the wanted level before hitting the street, this is
best.
However, everytime I have passed this mission I've just outran cops,
busted through
the barriers, never used a pay n spray, just out ran, and deliver the
brothers home.

Sorry if this was a long solution but I have done this mission many
times.
Hope some of this helped.