I like to use Ultra Black on manifolds, water pumps etc. Hi heat isn't really needed here and the black blends in. On cork gaskets I use gasket shellac to glue in place, UB on the corners of oil pans. Exhaust manifolds/headers/collectors I use Ultra Copper.
I use Permatex Aviation gasket sealer on everything I can. On places where I absolutely have to use RTV I use Permatex. Ultra Copper mostly, but on stuff where it might be offensively visible (I don't like RTV) I use regular black.
When you buy RTV open it and put a sample dab on something. Make sure it's "smooth", no chunky feeling bits in it. And make sure it sets up the way you think it should in less than 20 minutes. The reason I say this is that sometimes you can get a bad tube. Why I don't know, but it happens, more so with off brand stuff but I've gotten a bad tube of Permatex once too. Some off brand stuff I got once I put a test dab of on my workbench 2 years ago. It's still there and STILL hasn't hardened up. This kind of thing you don't want to discover after you've assembled your engine.
I flat just don't like RTV. But I will admit there is nothing better to seal the ends of Ford intakes.
NAPA usually. You can find it at most chain parts stores but for some reason it seems to be hit or miss whether they will have it on the shelf at any particular store. I can never remember the part number but it comes in a round white can with a brush in the lid. Look for the word "aviation" in the name. I use this stuff for everything, it's that good. The only sealer I've used on my old Harley for the last 10 years. I hate oil leaks and have tried everything at one time or another. This Permatex is the only stuff I've found to reliably seal on old motorcycles that tend to vibrate themselves to pieces.
Another nice thing about this stuff is that it's not quite permanent. Ever put something together only to find you have to take it all back apart again for some reason. Most often with this sealer you can save your gaskets for reuse (if they are reusable types). I've done it many a time, very handy on the race bike in particular.