Basically, i will assume the try zone ends are kind of shit. So along the sideline, what is the better view, an upper, elevated section, or a lower section?

Yes - do not go behind the posts. It is hopeless. The only tickets l 've had for Twickenham have been behind the posts & it is no good.
Along the sides - there is not a lot to it - lower or upper . You just get a different view - depends what u like really. If u like to see whole game play - go up as high as u can - staying in line with centre of pitch. If u want to see a few lineouts & scrums close up then lower positions r better. If u choose lower - do not choose a mid pitch - go for the somewhere between 25 yard line & touch. Much more activity.

Right on the halfway line and in the bottom or lower levels. done it many times and it is awesome viewing and you can hear everything (big hits, players talking).

At halfway; halfway up the stand or enbankment.

you do not want to be in the front row, trust me, l went to the All Blacks and Wales in Hamilton (Joe Rokocoko is debut :P) and we were in the front row on halfway. l was psyched when we got there, until l realised that you can not see shit past the touch judge.

You want somewhere from 22 to 22, about 6-7 rows back from the front.

l have the best seats going l sit right next to the away team dug out so i'm right near the middle get a good view of all the pitch plus l can shout at the away team when there playing nasty lol. Warrington Wolves fan

Ive been behind the try line at landsdown road and to be honest l quiet liked that old terrace, it was elevated and you could see alrite but my prefereed position would be about the halfway line half way up to stand or terrace you cans see the whole pitch easy.

I'd avoid sideline seats.real fans know behind posts is the best.u can get a perfect view of the whole pitch and you can see defensive lines and running lines of the team