I see many versions of oracle 8i , 11g and 12c.
I am familiar with SQL Server 2012 and SQL.
Which version of Oracle should I start with?
Start with the one you expect to need to know first. If have access to or expect to have access to a particular version then start with the concepts guide for that version. If you have no database or potential database in mind then start with the 12c.
Start here: 11G 2 Day DBA
Best of luck!
Oracle 11g (R2) ends support 1/31/2015, although extended support is available for extra cost.
I’d recommend highly you start on Oracle 12c. If you’re a SQL guy, you wouldn’t recommend a SQL noob just getting into SQL should start on SQL 2008 R2, would you? You’d get into SQL 2012, or maybe even 2014.
If you just want to get up and running quickly and playing with Oracle DB, you might want to download a free Pre-Built Developer VMs from http://www.oracle.com/technetwork/community/developer-vm/index.html#dbapp. It’s a whopping 4 GB+ download, but you literally download it and start up in VirtualBox (or maybe VMware by tweaking) and you’re up and running in minutes. The VM you might be interested in is called Database App Development VM.