Easier done than said
“They can’t even boil water.” Who hasn’t heard that said of someone they know who couldn’t comprehend the difference between a chef’s knife and a mixing bowl? Well, technology has made boiling water a rather easy process today.

Electric glass kettle with lip spout
In fact, variable temperature electric kettles make it child’s play to have water at the desired temperature for whatever brew we may be contemplating. And virtually any kettle, electric or stove top, will obediently produce boiling water if that is all we want or need. Further, there are Zojirushi style boilers that will hold up to 5 liters of water at a given temperature throughout the day. And the traditionalists have the Japanese tetsubin that, in addition to hot water, injects an iron component into your favorite brew, or the clay kettle that often is heated over a charcoal brazier (this may add immeasurably to the aesthetics of a tea session but it adds little to the tea itself.) In sum, there is little or no excuse for not having water at the correct brewing temperature.
The etymology of the word “kettle” is interesting. It derives from the Old Norse “ketill” and the German “kessel” both of which mean “cauldron” (and hence the reference in the title to the song of the witches from Macbeth.)[1]
Testing your kettle mettle

Plastic kettle
Assuming a kettle is made of a good material (not plastic, please not plastic) they all do pretty much the same thing; provide hot water. And it is of no great consequence if the water is heated on a stove top or brazier, or if it is an electric model. So, what real difference does the choice of kettle make? Well a great deal is made by some about how a kettle pours; and that difference concerns spouts. For not all spouts, it seems, are created equal.
Open sesame

Round spout stovetop kettle with annoying whistle
There are three basic types of spouts found on kettles. The most prevalent is a simple open spout. Usually located towards the top of the water reservoir, this spout is often simply a round tube (often with an annoying whistle incorporated) or a “lip” over which the water simply pours. There is nothing wrong with these of course (the whistle aside), and they allow for a rapid pour of water over the tea leaves. However, they don’t easily permit the precision that many seek in their brewing.
Tea brewing gets goosed
Following the lead of third wave coffee aficionados many ardent tea lovers arrived at the opinion that proper tea brewing required the ability to have pinpoint control over the addition of hot water to the leaves. And, they followed the coffee drinkers further in adopting the “gooseneck” kettle for their brewing. Indeed, I was recently told by one that all reputable tea houses used “gooseneck” kettles and that anyone who didn’t would be laughed at. The first part of that claim is pure hyperbole for many fine tea houses don’t use “gooseneck” kettles and the second part is, well, risible.

Variable temperature electric “gooseneck” kettle
Unlike the simple open spout, the “gooseneck” spout is a narrow tube that extends from the lower part of the water reservoir and flows up and out in two gentle curves. The narrow tubing allows for a slow and precise pour of the hot water.[2] That is its great advantage. But it also it its great disadvantage for it is not possible to get a quick splash of water using a “gooseneck” kettle. This is particularly important when doing formal comparative cupping of teas where a speedy pout is essential to achieving reliable results.
Some also contend that, due to the slow pour, the “gooseneck” design allows the water to cool significantly during pouring. Although there may indeed be some heat loss, I suspect that this is not significant.[3]
The “gooseneck” style kettle was designed for brewing coffee in a “pour over” fashion where some precision in handling the pour is desirable. Nonetheless, it is not an essential item however nice it may be to have one. Much more important is good quality coffee.[4] The same can be said for tea, using high quality is the most important step to obtaining an excellent brew.
Anything will do in a pinch

Old “pinched” style spout
The third principal type of spout is, in fact, very traditional and can be found on kettles old and new around the world.[5] Like the “gooseneck” it joins the water reservoir on its lower portion. And like the “gooseneck,” although less dramatically so, it is usually curved to some extent. Unlike the “gooseneck,” however, the spout is not a thin tube but a rather wide one that is “pinched” so that the opening somewhat resembles an inverted and elongated teardrop.[6] As such, it has a wider opening toward the top and a narrower channel at the bottom. This design offers the ability to pour quickly into the brewing vessel or to do so in a more controlled fashion but without quite the same ease afforded by the “gooseneck” design.

Electric “Stout Spout” kettle
Rochambeau
So, what conclusions ca be drawn from this brief recounting. The first, and most important, is that you should choose a kettle that works well with your particular needs and style of brewing. There is no single “best choice.” That said, however, we come to the surprising (to me) conclusion that the “gooseneck” design is the least flexible of the three; it only allows for a slow pour over the leaves. Either of the other two can be used to pour slowly or quickly although the round spout requires a good deal of practice in order to do so consistently. The pinched spout offers a very acceptable compromise between the two. I own all three types of kettles and use them all as well. That said, the “pinched” is, in my opinion, the clear first and it is definitely the style I use with the most frequency.
That’s my take. What’s your view?
[1] Wikipedia, https://en.wikipedia.org/wiki/Kettle
[2] “Using a Gooseneck Kettle” http://www.manualcoffeebrewing.com/using-a-gooseneck-kettle-for-manual-coffee-brewing/
[3] A “tea friend” in Chicago currently is doing an analysis of precisely this point.
[4] “Using a Gooseneck Kettle.” They also argue that a quality coffee grinder is far more important than a “gooseneck”.
[5] This form is ubiquitous in tea houses and merchant shops throughout Taiwan and China, for example.
[6] The “pinched” spout also is referred to as a “stout spout” by one manufacturer: https://www.mybrewista.com/products/stout-spout-variable-temperature-kettle
I currently use an open kettle that looks like a cauldron.
Stovetop kettles are much slower than electric kettles. Unfortunately, I’ve never found an electric kettle that’s not made in China. I have found a few stovetop kettles that are made in Italy and Japan.