Get the V8 for longevity and less repair costs. 

V8 is usually the best way to go. Especially if the engine is brand new like the new Tundra. But considering you are looking for a Lexus I would imagine it will still be more reliable than the competition.

If you intend to keep the vehicle for as long as possible until the wheels fall off, definitely go with the true and tried V8.  Also, with an all-new design of a new generation, it is usually best to wait a few years to see how it holds up before plunging in - even with Toyota’s and Lexi.  Now if you plan to lease, then it doesn’t matter as much.

V8 will likely have higher resale, if that matters to you.