First off, I have absolutely no medical knowledge at all, so please don't take my advice until you talk to your doc.

As a current preggo (though only for a few more weeks!), I've been looking for vibes that work well and are safe, too. I'm a little wary of g-spot vibes, just because I don't have a very good idea of my internal layout, and I'm a little afraid that my husband might end up hitting my cervix with it. (Why yes, I am paranoid.)

We tried the We-Vibe 3, but were mostly unimpressed by it (mainly due to it not fitting our anatomies right, me thinks). The g-arm on it is smaller in size than the average internal vibe, so I think it would be safer, but again, it just depends on how you're built.

I seem to have luck by wedging a bullet/egg vibe between my clit and my husband during penetrative sex. (It feels great on my end, but he has a hard time lasting more than a few minutes with it there.) As a general rule of thumb I imagine clit vibes would be the safest bet.