priests are very useful, you just don't need that many of them (besides the FoL blooming priests playing as the elves, you need quite a few to get your entire territory forested in decent time).
The recon line is nice, expecially for the civs with specials in the line (Svalt, recon UU's). They're fast, with decent strenght, and can easily exp up on barbs if you get them early enough.
War elephants have gotten tougher to get with the nerf to rangers. They're fun, but hardly worth the hassle (185 gold is a lot, even with mitigation worth well over 100 beakers, or putting your tech rate at 0 for a few turns).
Battering rams are redicilous, just bring a trebuchet instead.
Archers are units i seldom use. I never research the tech myself, and only get it through trade with a bottom-score AI or the eyes & ears. They're nice on the defence, but a purely defensive unit isn't of that much use compared to a multi-purpose unit like an axemen, a hunter, a priest or a mage (even though you should compare the latter one to rangers and longbowmen instead). I wouldn't know how to buff them though, besides granting the techs some economical benefit.