Hi
I use a lot of Nraas mods. I won't play without Relativity! That was the first mod I ever put in my game. Many of the other mods they make became became essential as well after that. It sorta depends on what you want to do. I use a lot of mods from MTS as well as other places that makes things easier or harder depending on what I want. An example icarus allsorts at MTS has a set the table mod that allows a sim to call the other sims to the table so they all eat at one time. I use a lot of his mods.
As far as builders go, yeah I have a few of RuthlessKK as well. :) This is the DNA team's thread and under 'Our Services' is a link to their blog site with all the builds from members past and current. They are awesome builders and will even build you a custom home if you want. I like trying to build my own places, but for fancy homes I've downloaded a few things off the blog.
http://forums.thesims.com/en_US/discussion/934382/d-n-a-request-team-designing-nature-architecture-just-for-you/p1