miranda 0.6.5: ~1.1meg download.
trillian 3.1: ~8.58meg download.
Additionally, trillian needs to download extra support files for the necessary protocols - ~245kb for icq/aim, ~211kb for msn.
The trillian installation takes a fair amount of time, it almost seems as they added Sleep() calls to make it seem more "important" than it is (why would DirectX or QuickTime installation checks take around half a second each?)
Trillian loads relatively slowly, the interface is skinned (and doesn't show window contents while being resized), has OfficeXP style menus, et cetera.
As for memory usage with ICQ and MSN protocols loaded:;
miranda: 5000kb private bytes, 560kb working set size
trillian: 31.344kb private bytes, 26.288kb working set size.
Oh, and trillian doesn't even support MSN custom emoticons.