For speedlights, you have to decide if you wanna drive stick or automatic—AKA manual or TTL. I live in manual mode, which means I sacrifice some convenience for reliability and repeatability. It also means I can pay about a third as much for each of my flashes.
If you live by TTL, you will die by TTL. Or, at least your wallet will die a small, unnecessary death every time you need to purchase a flash.
For manual speedlights, I wholeheartedly recommend the LumoPro LP180, about which I go into far more detail here. It's built like a tank, syncs four different ways, has a fluid and intuitive user interface, a built-in light-stand socket, a built-in gel holder and has a two-year manufacturer's warranty. No other speedlight comes close to claiming all of those useful features.
That it costs about a third as much as you would pay for an OEM branded flagship TTL flash is icing on the cake. If you can commit to shooting manually, this is your flash.
If you need TTL (and remember, this is the gear acquisition equivalent of joining the TTL mafia) I would consider eschewing the OEM flagship TTL flashes. They can run north of $500USD, which is just nuts.
The Phottix Mitros comes in Nikon and Canon variants and sells for about $300USD—with twice the warranty length. It does pretty much all the fancy stuff most of the OEM flashes do including the optical TTL triggering of other TTL units, be they other Mitros units or OEM units.
I will say that for the lesser price you will give up some ease of user interface. But this may well be that I was used to the OEM flash user interface and that of the Mitros is pretty radically different.
Finally, for some people the flagship OEM flashes will be just fine. For instance, if your name is Bill Gates they are a perfect choice for you.
On the opposite end of the spectrum, there are a ton of flashes constantly hitting the market from the far east, from a variety of pop-up brands. Some of the brands are recognizable because they bought the rights to use familiar but now bankrupt brands that were formerly trustworthy. They have spotty track records for quality. Factory warranties are short to nonexistent.
Many who read this will be tempted to go that route because of prices that are almost too good to be true. If that's you, by all means knock yourself out. Some people need to be stung in the wallet to remember a lesson or bit of advice. I know I did when I was young. Good luck with that!
As far as big lights go, there is a completely different set of variables to consider. Big lights are system-oriented, and you would do well to choose wisely in what will likely be a long-term relationship.
I spent a lot of time and money auditioning big lights over the past 25 years. I am really happy where I am now, and would have loved to make this good of a choice from the get-go. I wrote about researching and choosing big lights a couple years ago and at the time settled on a Profoto/Paul Buff hybrid choice.
I loved Profoto's light mods and quality of light, but they were very expensive. And the battery options insanely so. So instead of battery versions of my Profotos, I went with Profoto plug-ins and a full Paul Buff Einstein setup for portable, battery-powered big lights. Sounds crazy, but for the price of just two AcuteB battery generators you can outfit yourself like an Einstein King.
So for the last couple of years I have had two full systems in my gear closet: Profoto plug-ins and Einstein 640s with portable battery packs. (But they also plug in.) And even though the Profotos are far more expensive, rugged and "professional" (whatever) I found myself again and agin choosing the Einsteins to use.
That's because inexpensive or not, they are simply amazing flashes. And they come with a 2-year warranty (sensing a trend here?) and legendary factory service. Further, Paul Buff has finally taken some time to develop the modifier system that a good flash deserves. The reflectors and accessories are well-designed—and wonderfully inexpensive.
The caveat here is, this is pretty much a US-based choice/suggestion. One of the main reasons Paul Buff lights are so inexpensive is that he only sells direct, and mostly in the US. There are a couple of dealers outside the US but that starts to erode the value proposition pretty quickly.
So, to beginners looking for a great light at an amazing price in the US, I would suggest you strongly consider Einsteins. Not the similarly shaped and even cheaper AlienBees, however. They look similar, but are not in the same league as the Einsteins. Save your money and go Einstein. It is not that much more.
If you are outside of the US, I am sorry that this choice will be either not available or not nearly as good a value to you. So I would suggest that you look at other reputable flash brands (Bowens, Elinchrom, Hensel, Profoto, etc.) and choose the brand that works best for your needs and your wallet. This advice also holds for people for whom the Einsteins aren't a good fit.
Again, I would suggest avoiding the temptation of the super-cheap mystery brands from the far east. Personal experience. But if you need some personal experience of your own to dissuade you in the future, by all means go right ahead.