Best Sherman m4 for my second project?

New to WW2  modeling -- but how are you at complex and delicate parts (albeit very accurate)?  Or would you like another go at a Tamiya (i.e. good engineering, good parts fit, good instructions, solid but not super detailed/accurate)?

If the former, then I recommend a Tasca/Asuka Sherman kit (for an experienced modeler).

If you want simpler, then go with Tamiya M4A3 kit  or Tamiya M4A3 (105) "assault" tank (just leave off the add-on side armor).

Or the Italeri or Academy 1/35 Sherman kits are in the same league with Tamiya regarding assembly ease, detail, parts count, etc. They are a tad bit more complex, but still easy projects for the newer armor modeler.

Hands down, Tamiya's are the most builder friendly, like Roy said. The complexity increases a bit with Italeri, but then again, nothing over challenging at all. I built my first of those when I was a far less skilled teenager many years ago. The Academy kits have the advantage of being newer moldings, and have a less complicated suspension than Italeri, but are not really more complicated anywhere else. Painting any of these kits presents the same challenges, which are completely separate from build issues. And an overall Olive Drab paint scheme is pretty easy to handle on any of them. Good luck to you!

 Although it's been a while, my last build was a Sherman M4A3E2 Jumbo . 

 That build was a conglomerate of spare parts from different kits and web searches.

 With a bit of patience (what this hobby is about), imagination and ingenuity

..... you can actually save money and build a nice subject with parts from multiple kits.

Do any of these models include a full engine? What about interior detail?

The only M4 kits I can think of with interiors and engines are the old 1/48 Bandai kits. Long OOP.