Depends on mods car already has...otr/extractors/tune + diff gears is enough to keep most people happy.
Next step is valve springs & trunion upgrade for those that want to rev ringer out of them.
After that is cam/stall convertor and/or heads that will make mince meat of the auto.
Comes back to age old questions...
What mods currently?
Budget?
Daily driver or weekender etc?
Budget?