Before you buy, I really recommend checking here first. Say what your budget is, what you want to use it for, the paint you're thinking about and you will get a bunch of great advice. Everyone has their faves, but at least you will know A) that what you're buying is suitable for the task, and B) if the quality is good enough both to learn on, and for your needs.
Without knowing any of the above - I recommend looking into the Iwata eclipse range. They have a side feed if that is the kind you are interested in. Not cheap - but far from the most expensive, and more importantly, IMO it is the best performing brush for the money that there is, the most reliable and well made, with the hardest wearing parts. It is the industry workhorse, an all rounder that can give super fine detail (when you get to know it of course) and a 2 inch spray pattern for larger work. It makes learning much easier, the nozzle size, as it's not strictly a detail brush, is a little larger, so is a little more forgiving while learning paint ratios. This is not a brush you will outgrow, as it really is capable of super fine detail (not as effortlessly as the microns, but it can do it), so the money spent now is a good investment, as you may never need to buy another - though if you're like most around here, you will probably want to
. Well worth shopping around as price can vary a lot, and see if you can get vouchers for places like hobby lobby, who I believe do %40 off.