Long story made short, if you were starting off from scratch and wanted to get up and running as quickly as possible, would you start off with autocad MEP or revit MEP?
If you have never touched Autocad and you are solely doing engineering work then I would consider using Revit instead of Autocad MEP. Revit is more geared towards the engineering community and has many tools that help in the design process. It is vastly different than autocad mep in that it was designed from the beginning as a modeling progrom where autocad mep is buit on autocad which is a pure drafting program. i.e. it was originally built to simulate drawing lines and circles.
I forgot to add that you can download free 30 day trials of each piece of software and give each a try. You might want to install them at different times though so you have enough time to test each one. Autocad MEP has a tuturial you can download although it is for a 2010 version. I am sure that Revit MEP has something similar.
Notice, Personal Rant below
As an Engineer, I dislike REVIT. I worked for a contractor so I may be biased. If you are starting your own company, like I did, PLEASE be aware that REVIT is NOT backwards compatible with itself. This happened to me, and I was lucky I had an upgrade clause in my contract.
Long story short, we were using REVIT MEP 2010. Architect Upgraded to 2011 because they (large firm) was on subscription. So they migrated up!. Guess what? The architect bought all of the engineering subs an upgrade to 2011 (was nice for me).
There are more tools and content in REVIT, than MEP; however, I have yet to be able to justify the price. I can get more 3rd party add ons for MEP that fill in the gap for builtin functionality in Revit. ALSO, I have seen a demo (East Coast CAD), where a plugin is able to migrate intelligent items between Revit and MEP (I Have not used it).
Long story short ... I stayed with AutoCAD MEP and use REVIT only when contractually obligated. The Mechanical contractor and even the owners require DWGs and crushing a REVIT drawing is just re-diculous.