Basketball is a much bigger sport in Europe than American football (not to be confused with the futball that rules European sports).
However, in reality, the NFL is far more likely to put a team in London than the NBA. Logistics is why, and why the NBA is much more strongly considering a team in Mexico City (there will be a D-League in the Mexican capital within a season or two).
Adam Silver addressed the NFL’s scheduling advantages for a London team, speaking to Marc Stein of the New York Times.
For the NBA teams closest to London — Northeast teams such as the Knicks or Celtics — the flight time from their cities to London or Mexico City are about the same (a little over six hours). However, for a team such as Miami it is just a little over 3:30 to Mexico City and nearly five hours more than that to London. And as you move West and get to teams from Los Angeles or Denver — not to mention the three teams in Texas — the trip to Mexico City is less than a cross-country flight to play those East Coast teams.
I could see the NBA putting an All-Star Game in London someday, but even that would require a longer break around the showcase game than exists now.
I’m not about to speculate how an NFL team would draw in London, if they could sell out the required luxury boxes and expensive seats, or if they could help broaden the league’s shrinking television audience. But it makes a lot more sense for that league to explore the idea than it does the NBA.