First, I'm not doing stuff usually the "normal" way... far from it...
But I can write about how I do this! read on if that sound interesting...
I usually like to listen in mono when comparing, first. (Try this!!! Start with mono, one speaker!)
I get up, stand real close to the pairs (they are usually then both connected, placed side by side, the old left + the new left, I also place the old right and the new right on "its" side...)
Then I put my head right up there at the baffle of one speaker (I don't play loud...

)
Move my head up and down a bit to hear the drivers.. Then to the other speaker just beside it.
Move a little more away, then some more, until the drivers "blend"..
Then repeating this I unhook the old ones, and listen to only one set..
After doing this.. I get about longplay sessions with the new set... then with the old, and quickly back to the new set (sitting in my chair ..the sweet spot you know.)
I need to know how the speaker sounds in mono first... before moving into the stereo sound. Unusual?
I don't know. and I listen to the left channel first. Usually.
But I have found it gives a really nice view of the soundstage abilities of the "pair" once you have done this. And the center fill ability, image height/solidity, Instrument placement... It all just comes to life this way I feel!
It also, at lest for me really helps with finding the placement in the room.
Is this a proper tech? Again I don't know!
I find that I can pick up just about any difference between the pairs with this approach.
The new pair goes EXACTLY were the old one was when AB'n ... I mean usually that's the spot in the room were most speakers will at least shine "somewhat".. And you can tell apples from apples...

OK. Comparing two speakers of very different design types.. that would be different...
I'm sure (floorstanding/dynamic) is what we talk about here.
I try to walk the soundstage, move my head around...listen for lobing such as that.
With ones old pair, you get out of the chair, change tracks, or with a remote you maybe need more beer after a while... hehe. Do you turn off the speakers? I would hope not!!!
That's why I also leave the room when comparing! How does it sound from another room?
When I get up and sit down... walk over to the rack, Bend down behind to inspect the cables... stuff like that...
Imperial