Which one is more versatile and better functioning program for custom content creation/mesh editing ? i am trying to mod Sims 2 and 4.

I use both. Blender for meshing and UVmapping, and Milkshape for small adjustments, bone assignments, making custom thumbnails (pictures) and checking recolors while I'm working on them, among other things.

Blender is the most useful one for the actual meshing, but it can be difficult to learn and the menus can be very confusing, plus if you don't export the meshes correctly you get errors in SimPE (particularly OBJ meshes).

I much prefer Blender for static meshes and UV mapping. For me, it was a lot easier to learn than MilkShape.

It's good, however, to have a copy of MilkShape and familiarize yourself with using it. Particularly if you need to work with meshes that have joints, or if you want to mod clothing and accessories. There are a lot more plugins available that make it specifically compatible for Sims modding.

Blender has a steeper learning curve. It's not intuitive, at all (the newest blender is easier for a beginner to use, but it's still in beta mode), but once you get the hang of it, it's a lot more flexible than Milkshape. There are plenty of tutorials on youtube that teach the basics. But I'd echo what everyone else said about being open to both. Most Sims 2 meshing tutorials are written for Milkshape, plus as mentioned, there are more TS2 specific milkshape plugins than blender plugins.

You don't really need a TS2-spesific tutorial to mesh objects for TS2 with Blender. Find good modeling tutorials, extract a model from the game you can use as a size reference (for chairs, tables, etc.), and worry about getting the object ingame when you're done with the meshing.

True, you don't need one, especially for the simple things like static objects, but I think it'd be easier to pick up working with things like clothes editing/conversion or when there's a Sims 2 specific tutorial available.

For clothes and other bone assignment or morph projects, you do need a good sims-spesific tutorial, and it's easier to find them for Milkshape. There may be as much as one or two for Blender...

There's a set of plugins for Blender that lets you do bone assignments and all that - but I have yet to try it out, so I can't say for sure how well it works.

I'm used to work around the programs I've got available, so I know which one I get the best/easiest result of doing whatever I'm doing. I may use two and occasionally three programs (I also have WIngs3D, though after I managed to get Milkshape to work on my laptop I only use it for finding accurate slot placement. I used to have 3DMax, which I honestly prefer out of all of them).