I attached a photo of my winter scene that includes many of the items from Lionel and Lemax you are considering. There is definitely a difference in scale. Lionel is O scale, but the Lemax items are larger (don't know exact scale). For that reason, I put the Lemax units in the foreground and Lionel units in the background. The different perspectives help a bit. FYI, I remove the Christmas items after the holidays so that it is more generic.
Hope this helps.
Michael