I think that I know what you mean. You define a thru-hull as the fitting that goes through the hull and to which you can attach a valve of some sort - like a ball valve. You seem to define a seacock and an integrated through hull fitting and valve. If I'm wrong, stop reading.
I personally like tapered Spartan seacocks because they are serviceable. The ball valve, while very reliable is not serviceable (at least in my experience). If anything happens in the way of a leak, you don't have much recourse. Since there are two parts to join (the through hull and the valve), it's just another area for a potential leak. I've serviced my Spartans many times with grease and occasionally with valve grinding compound (in the rare event of a bound seacock). You probably already know this, but do not use a gate valve anywhere on the boat.
IMHO, REALLY humble opinion, this is definitely not an area to save money. I am absolutely rabid about leaks, especially those below the waterline. Since I like to sleep at night, I'd spend the bucks to get the best, like Spartan, but there are others.
In the interest of full disclosure, I'll admit that the raw water cooling inlet to my A/C unit has a ball valve that I plan to replace. Whoever installed the unit used a ball valve and modified garden hose. I installed reinforced hose; the valve is next.
Y'all - Please don't jump on me about this. I know that many manufactures use ball valves and the boats float, but I really like to be able to inspect, grease, and adjust my seacocks. Just my $0.02...