I am finding myself fishing a lot more streamers on medium sized western rivers (i.e. Bighorn, Yellowstone, Missouri, Green, Snake, etc.). Some of the newer, big (and sometimes heavy) streamer patterns and fast sinking sink-tip lines really seem to overtax a 6wt rod.
Been fishing/testing several 7wts and a couple of 8 wts. Haven't quite found nirvana yet, some too stiff, some too soft, some just ok. Probably will find a rod or two that I will get along with eventually. Actually, it is kind of fun trying different stuff.
I have tried the following during my search ( some just casting, some fishing and casting):
How big of streamers are we talking? Several inch long meaty articulated stuff with lead eyes? Or smaller, more reasonable stuff? I briefly had a Sage Largemouth that could throw anything I asked of it, and then some...it was just too much rod for what I wanted to do. Recently I have got into spey rods and have found them to be able to throw some pretty meaty streams a long ways. If I am swinging a streamer or want to get down deep, nothing beats a spey rod. If I am stripping streamers, a single hander is the way to go. For reasonable size stuff I use a fiberglass Steffen 8'6" 6wt. I am on the lookout for a Steffen 7 or 8wt that will really be able to throw the big nasties. This is not your grandpas fiberglass. It is med-fast and actually bends when you get a fish on, unlike some of the latest and greatest ultra fast rocket launchers. I would give a glass single hander, or a spey rod a try.
I've got an Orvis Hydros 906-4 tip flex that is a beautiful streamer rod. The Hydros series was discontinued a few years ago, but I'd guess the current Orvis Helios 2 or Hardy Zenith or Loomis NRX in a 9' 6 wt would be as good or better. I have tried the TFO BVK and Winston B3x and didn't like them as well. Have not tried the Sage One or Circa, but I have heard that the One is difficult to cast and the Circa has a soft action. (I think a crisper action makes a better rod for streamer fishing.)
If you are throwing a rig that a 6 weight can't handle, you're doing something more specialized than most streamer fishing.
Between the great Loomis, Sage and ECHO3's you have tried and the Hardy Proaxis and Scott S4s that has been mentioned, I only have one ringer to throw into the high class mix...read my post in Tackle Reviews about one of our forum members #8 rod, the Flying Pig.
I've been tying & fishing with streamer flies for many years and cannot narrow my preferences for rod down to one or 2. I use every rod I own for streamers. Choice revolves around the size of stream to be fishing on and mood on any given day.
When I go to a small creek near our home I sometimes take a 6'6" bamboo 3 weight, other days I use a 6'3" graphite on that same creek. When I go to medium creeks that range between 30 - 50 foot in width I'll sometimes use either a 7'9" Orvis 5 weight or a 9' Orvis PM-10 in five weight. Same creeks on a different day.......8' six weight bamboo.
With those rods a fellow can handle flies up to a size 2 or 4 long shank hook without weight on the fly itself. When I fish rivers, I'm more likely to have a 2 hand rod in 7/8 weight because they are more efficient for the big water especially when you are short on room for back casts.
While there may be one rod better suited for streamer fishing, a fellow can use whatever rod he likes or owns to do it. You may need to take some time to develop your personal style for casting and controlling the fly once it's in the water but you can adapt to nearly any rod you may buy or own for fishing the wet flies.
Perhaps it is best to find a rod that satisfies the general fishing conditions where you live & fish most often. By doing so you can adapt to whatever comes along during a day on the water. Even though I love streamer fishing & do it 90% of the time, it's nice to know that should I blunder into a stone fly hatch that resembles a snow storm, I can simply change leaders and take advantage of the surface action for awhile.
So........... My favorite streamer rod = all my rods.