My fly line preference is for a profile with a continuous front taper. There are a number of these on the market and some are better that others. I really like the Royal Wulff Triangle Taper Nymph (previously reviewed), The Rio Single Handed Spey and Barrio SLX. Each have their own combination of compound tapers but all fundamentally act in the same way. They have a fairly short, continuously tapered heavy head with the bulk of the weight at the back. This makes for a great line for roll and spey casting and gives the opportunity to shoot a considerable length of line when overhead casting.
The big difference is the price and quality. The SLX doesn't come with welded loops (I always cut these off anyway) and the duo colour isn't as good as it could be. The colours bleed into each other and don't clearly define the end of the head. But it's almost half the price of the competition and really good value.
The SLX features a head length of approx 33 ft with a series of compound tapers, a short belly and short rear taper . It's designed to be heavy on the scales, but feel light in the air. However be aware when overhead casting that this is a heavy line and compensate accordingly.
The SLX has two colour options, an orange head with tan running line and an olive head with cream running line.
This is a good line at a very reasonable price, I use it for fishing, instructing and casting demonstrations, and frequently recommend it to clients. I have found the service from Mike Barrio to be excellent and lines are usually delivered within a day or two of ordering.