If you don't want to splash the cash on a Vortex you can get shakers designed for agitating nail polish bottles of eBay for ten bucks. Still does the job perfectly. You might have to run it a minute or two longer but it has always worked unless the paint is beyond use.
I usually recommend people get a few paints of the brands they are interested in but the flaw in that advice is that each brand has its problem paints. You might think that a certain brand is crap but you just picked a bad colour or that you like one bottle but the rest of the brand is rubbish. I've found that out the expensive way. A brand that suits someone else's painting style may not suit yours so take everyone's, including my advice with a grain of salt. Personally I love VMA and VGA paints as the way I paint I use that translucency to my advantage. Most people dislike the VGC and VGA yellows and greens etc but I love them. I've bought a box of Scalecolour and disliked them so much I've never used them since. You need to choose one or two from most colour sets rather than one or two from each range.
I've found P3 paints to be the surprise gem due to the liquid pigment they contain rather than fine pigment particles suspended in binder.
Keep in mind the other brands of paints that military modellers use like Lifecolour, AK Interactive and Mig AMMO. The themed sets with acrylic paint and pigments are great. More and more I find myself going to those when I'm painting figures.
MAxx is right in saying you have your favourite colours and tend to waste the rest if you buy an entire paint line. Pick a mini and then buy a few paints you know you will definately use on it rather than buying the paint then trying to find a way to use them. It's a false economy if you buy an entire range due to the cheaper overall cost if you only use a third of the colours.
I don't mind spending the extra money to get the Vortex, I personally don't trust a plastic mechanical shaker from china for $10 to last very long. I'll be able to use the Vortex to shake other things in the long run as well, I bet it works great with spray cans too.
As I said before, I understand the idea of getting only "the paints you use", but for me that's really quite hard. I sat down this week and went through the scalecolor range and picked the ones I wanted going "That one.. and that... and that... and that..." and I still ended up with paints for 150€, so the same amount it costs to just get the whole set more or less.
I think I might need help or at least some kind of guideline as to what colors to get, and not to get if hand picking is going to be an option.
I got a hold of two Reaper colors this week from an online store, and tried them, seem quite good - definitely more coverage than VMA and dries matte. The stocks were poor though and the reaper paint sets seem very large and not that diverse if I'm not mistaken.
This coming week I should be receiving paints from Scalecolor, Fantasy & Games, P3 and DarkStar for testing, really looking forward to getting some experience with them to base my purchasing decisions on.