Neither. Lennon sounds too much like Lenin, a very different and much less appealing historical figure. Bowie named himself after a hunting knife and pronounced it wrong. To this day, people pronounce both the knife and the singer’s name wrong constantly. Both are surnames which I hate as first names anyway.
I would go with John or David if I HAD to name my kid after those rock stars, but honestly those are so generic I’d probably just skip it.