I've found a situation where I can't decide what to do. I like confronting Taggart during his speech, but I also want to plant the evidence on his PC and frame him - but I can't do both. Does one give more benefit than the other (apart from the speech one giving an achievement/trophy)?

There's no right or wrong way to play the game. It's all about how you feel you should proceed. If you think Bill Taggart deserves to be framed for what he may or may not have done, then do it. 
 
I chose the speech every time, though. I love making him look like an asshole.

i never confronted him, just because of the path i was on. i ended up digging through his computer but did not plant the evidence.

How do you get the option to plant the evidence? Do you get it after hacking his PC?

Because I didn't go throught with that. Only had the option to hack in for the info or talk to him, didn't see the plant, so wandering it when you get it?