ExpressCheckout is designed to be used in concert with a direct credit card acceptance method (such as PayPal's DoDirectPayment, or a non-PayPal credit card acceptance method), although it can be configured to also do guest payments. This is why the demos of the normal configuration handle only PayPal account creation; that's the normal usage.
One key question you need to ask yourself is whether you want to have access to the credit card information & be the "merchant of record" yourself or not.
YES: Doing this gives you the most flexibility, but will require you to go through some merchant vetting and carries some security obligations (PCI) even if you are using some solution which tries to distance you from the actual raw card numbers (e.g. collecting them via PayPal or Braintree code and immediatly encrypting & tokenizing them). In short: if you want full access to the card, then you have legal obligations re: handling that account access which technology can reduce but not eliminate.
NO: If you are content to always treat your customer's card information at arms length through PayPal, via the legal structure of a PayPal account (whether the user actually has a PayPal account or is just doing a "guest" payment on PayPal where they give PayPal their credit card for one-time use) then you can reduce your vetting & security constraints (no PCI requirements at all).
If you want (or need) access to the customer's card [YES above] then the "classic" API solutions are either DoDirectPayment (for when you collect the card info) or Hosted Sole Solution (for when PayPal collects the card info on their page). HSS meets all 3 of your requiremens above; DDP fails requirement #1.
If you can live with access to the customer & the payment but NOT the card account itself [NO above] then you can use Website Payments Standard, or EC with Guest Checkout option; both meet all three of your requirements.
All of the above solutions are not only still supported, but have tens or hundreds of thousands of integrated merchants and are the biggest/mainstream ways in which PayPal payments are handled.
If you prefer the newer products & are in the first category above (real card access, not guest payments) then you can also use Braintree or the RESTful APIs. These newer products don't yet have as much flexibility & coverage as the older products, but hey, less complexity can be a good thing as long as they have what you need. These products are generally designed around plugins for your web pages rather than entering card information on PayPal's site, however, so they don't meet your first requirement.
You can also do PayFlow (several variants) or Adaptive Payments or or or.... but in general I would advise picking either the most well-established or the new-and-growing options as being better supported & more future-proof.
