Choosing which fly line is best for your purposes can be a difficult decision. These days many manufacturers sell their lines, & describe them to the consumer, based on the fishing situation the line is designed for. It wasn't always this way & at first I thought this type of marketing was just a ploy to sell more fly lines. However, I've come to realize that these lines for specific types of fishing may not be a gimmick after all. Let's consider that for a moment.
In the fly line industry, line weight is determined by the weight (in grains) of the first 30 feet of line. After that 30 feet, line makers are can taper their lines anyway they want to. Plus, different manufacturers make lines with different cores that effect the line's stiffness & different coatings that effect the line's slickness. All of this, naturally, can change how a line casts dramatically. So you see, not all four weight lines, for example, are the same.
Is there a particular brand of line I recommend? No. If you ask me I'll tell you the kind & type of lines I use for the type of fishing I do, but I don't endorse (or design my rods for) any brand of fly line. Bottom line, pun intended, is that you have to ask around & try out different lines to see what will work best for you. Do your research.
I also get asked which type of line is better to use, weight forward (WF) or double taper (DT). My answer is that it depends on the type of casting you'll be doing. For shorter casts of 10 or 15 feet, it doesn't really matter - both will do fine. If you're going to be doing a lot of roll casting (like I do) than you're going to want a DT line. DT's roll cast better than WF's because the WF'S don't have enough weight, or mass, behind the tip of the line to roll out line in a roll cast easily. The weight in a WF line is all at the tip of the line, not behind the tip, like in a DT.
For long casts where you'll be shooting out a lot of line, the WF is better & easier to use. I always say that if you're going to be putting a lot of line in the air (to measure your cast) go with a DT. If you'd rather shoot the line out, rather than put it air born in your false casts, go with a WF line.
So basically in theory, WF lines shoot out line a lot easier, but DT lines roll cast better & are a little easier to aim. For beginners I suggest a DT for those reasons. If you're an experienced angler than go with what you know & what suits your casting style. To each their own.