Surprisingly, a lot of reptile-keepers I talk to, dislike BPs. They complain about their finicky appetites; their shyness; etc. I think it is BS; if you're a true owner, not merely a dolt who wants a snake for novelty, you have the patience to wait out a fasting snake; care for them through thick and thin, etc.
Personally, having a few BPs and one RTB, I would hesitate to recommend a boa to a beginning keeper. They just get really big, comparatively, fast. They need a lot of attention and are just different than BPs in many subtle ways; much mroe likely in my experience to strike-out, thinking you're food, though I know Bps can do that too; but I'd recommend getting a BP first, to get experience handling and keeping boids, before getting a boa. And an awesome idea, would be to get a larger, maybe unwanted boa later on, instead of supporting the pet trade by buying a smaller one; there are so many unwanted ones on a lot of reptile- rescue sites.
But, if you're set on wanting a boa, not really a BP, I would not suggest getting one merely as a stepping stone; maybe a smaller boa would do.