There are alot of great machines out there for you to choose from. Buy the best machine that fits in your budget and consider what projects you plan to use it for. Another thing to consider is what attachments come with the machine you're considering and whether you'll use them or not. For instance, if you're going to quilt, you'll need a free motion foot/walking foot. Some of the best seamstresses I know say they rarely use all the stitches available on their machines.
I own a Brother machine and I love it. It has 60 stitches and has sewn beautifully since I bought it. I also sew on a Bernina and love the the ease and quality of the stitches but this is a high end machine.
As for threads to use, don't buy the 5 for a dollar spools - those won't hold the stitches well and your thread will break often. I use Coats and Clark and a few other cotton/polyester threads.
Often you have to try different threads with your machine. A good thread may sew great on one machine and not on another. Buy two types or brands to start with and test them on your machine is my recommendation