Different heads make different amounts of horsepower at different rpm ranges...and since horsepower is a product of torque, different amounts of torque at different rpm ranges. So it depends on how you want to drive your car.
Personally There are the Edelbrock performer, the Twisted WEdge heads and so on. Different aluminum and aftermarket heads may not work with your factory exhaust manifolds or headers.
So I have to conclude with I like Ford's FRPP heads. They may not flow the best in comprarison to the modified heads offered by the competition (they do flow really well for a daily driver/every now and then racer) and do keep your ford all ford, and if you ahve any tech questions fords FRPP hotline is the greatest thing since sliced bread (IMHO). Look at the GT40P if you want Iron Heads, if you want aluminum look at the GT40-X/Y/or Z heads depending on the chamber size you want to run. Any of the aluminum heads are port matched to the Edebriock Performer RPM (hi rise) manifold or GT40 EFI setup.
The Iron heads I am not too sure about....but were available on the 93-95 cobras and have "exclusive" roller rockers just for the Cobra head which fit under standard valve covers (you dont need the tall covers) and the fulcrums are larger then any other roller rocker giving better longevity.
Then pick a camshaft that works well (flat tappet or Roller depending on your block coice) and top it with the recommended roller fulcrum and tip rocker arms and appropriate valve covers.
So much of high rpm horsepower is made in the head design (big valves and ports).
Similarly so much low rpm torque is also produced in head selection (small valves and ports).
I like big ports and smaller valves. The smaller valve size may be made up in Camshaft valve lift. So pick a cam that with 1.7 rockers gives you within 10% of the valves terminal lift (where binding occurs) and buid it with the 1.6 rockers and see how it run. You can add more lift by adding the different ratio rockers in the end as long as you have enough of piston to deck (or valve reliefs) clearance to run the bigger rockers and camlift.
As far as valve size goes. I have seen heads with huge valves (2.02-2.06) offered by different manufacturers that do not flow any better (actually worse) then smaller valve heads. With a 289 it is best to keep the valve sizes smaller to fit in the combustion chambers unless the valves are moved (which also moves the exhaust port location) to accomodate the smaller diameter cyclinder.
My Recommendation, stick with conventional wisdom.
69-70 351-w heads are the cheapest way.A minor port clean up and 45 hp can be gained, more if you header and intake correct.Call SCOTT 936-756-2535 . I need more info to tell it all here.ie:what pistons you have what cam etc.Call and I'll give you my 2 cents worth.I have a 351-w in a daily driver with 350+ hp with these heads.Don't spend the kids lunch money on aftermarket products.The factory built some sweet set ups that with a little work can zoom!!!!!!!!!!