today I made my first Oracle certification (OCA Java SE 8) and I passed it with a score of 97%.
Attached you can find the CertView view
What did I use to study? Principally the Mala Gupta book (it's really well done), but in the meanwhile I was waiting for the Mala Gupta's I used the Selikoff's (it's good but it doesn't retain the information as the Mala Gupta's does).
How much time did I use? 2.5 months, but I'm also working during the day, so let's say 1 month in the end.
Did you use any simulator? Yes, I used the Enthuware simulator and the Sybex simulator (just once), but actually the exam was much easier than the mocked ones.