I found the UK trades of the events are best
The Inifinity event stuff is split into two trades but has all the pertinent series contained inside.
The way they released in the UK is weird as hell though.
So you have
Avengers vol 1 TPB (#1-6)
Avengers vol 2 TPB (#7-11)
Avengers vol 3 TPB (#12-17)
Avengers vol 4 TPB (#18-23 INFINITY issues)
and
New Avengers Vol 1 TPB (#1-6)
New Avengers Vol 2 TPB (#7-12 INFINITY issues)
And then you have the two Infinity paperbacks that collect
Infinity #1-3, Avengers #18-20, New Avengers 9-10
&
Infinity #4-6, Avengers #21-23, New Avengers 11-12.
Notice that the two infinity paperbacks do not include New Avengers #7-8? So you would still have to get New Avengers Vol 2 TPB to get issues #7-8.
The other option, of course, is to get the Infinity hardcover that includes
Infinity #1-6
Avengers #14-23
New Avengers #7-12
However, although you can now skip the second volume of New Avengers, you have to get Avengers Vol 3 for issues #12-13.
TL;DR: If you get the two infinity paperbacks then you will end up rebuying New Avengers #9-12 (to get #7-8) and if you get the Infinity hardcover then you end up rebuying Avengers #14-17 (to get Avengers #12-13).