You've managed to squeeze in three questions for the price of one!
From the title of your post: What's the easiest way to get a good virtual piano? Answer: If you don't already have one in a DAW, the fastest and easiest way to get one is to download it from the internet. You can start with a free one, move up to an inexpensive one later if the free one doesn't sound good enough to you, and move up to a more expensive one later if the inexpensive one doesn't have enough bells and whistles for you. Alternately, you can download a DAW that has a virtual piano plus numerous other instruments.
From the text of your post, before the comma: What's the easiest way to play a virtual piano? Answer: The easiest way to play a virtual piano is with a MIDI keyboard controller. If you don't have one, you'll need to either click on a keyboard display with your mouse, or use your computer keyboard, neither of which is well-suited for piano playing. If you decide to buy a MIDI keyboard controller, you might be tempted to get a small one (2 or 3 octaves, possibly with mini keys), but those aren't so good if you want to play the piano with both hands or play pieces that span more than 2 or 3 octaves. They are, however, great for toting with you if you want to write music while you're traveling. For piano playing it's probably better to get a MIDI keyboard controller than has a minimum of 4 octaves, and preferably 5 or more octaves. And if you'd like to use the MIDI keyboard controller for more than just piano playing, you'll probably want to get one that has plenty of wheels, buttons, knobs, sliders, and pads.
From the text of your post, implied by the part after the comma: What's the easiest way to use a virtual piano? This will depend somewhat on what you want to use it for. If you're using it for live playing then a stand-alone program will probably be easier to use since you're cutting out the "middle man" (i.e., the DAW), hence there's fewer menus, buttons, and clicks needed to get to the virtual piano. But if you're using it for composing and recording then a DAW would be the way to go. Note that virtual instruments are often designed to function either as a stand-alone program or as a plug-in for a DAW, depending on your needs.