The best travel SIM is, and will be for a long time,
Google FI. I pay 70$/Month for the unlimited plan, which is really unlimited*. I never changed my SIM in any country, they are covering 200+ countries with voice, sms AND DATA!!! Now to the * : You have 22Gb at full speed, then it will be "limited", but not limited like nothing will work anymore, they limit it to a reasonable speed so you can still surf the web. Normal carriers limit the speed to an unusable speed, lol.... If you want to go back to full speed and billing cycle is not over yet you can do so for 10$/GB, but I never personally made use of it.
Here comes the great BUT.... but you have to order and activate the card in the US
. First activation outside the US doesn't work anymore. I was able to activate it outside the US, but a friend who ordered the card a year ago to my US post forwarder and then to him, wasn't able to activate it outside of the US.
But if someone is in the US for a few weeks, I can really recommend him to get a Google FI SIM.
Not part of the initial question but maybe still good to know:, for bank verification etc. i can recommend: onesimcard.com , they have a special virtual SIM for bank verification, just ask support. No verification needed, payable in BTC. I recommend them over proovl.com, because proovl has a lot of carrier issues.... at least 2 major issues with canceled numbers a year... once they canceled 10+ numbers over the weekend and wasn't able to react.... just imagine telling the bank to change 10+ numbers for which you lost access... At onesimcard never had any problems so far.