How easy any given class is depends on your playing style of course, but most people agree that valkyrie is the easiest class in nethack. They're good for fighting, they start with good equipment (+3 small shield means that once you've picked up some body armor, you'll have a very nice AC for a starting character) and food and they have a decent quest artifact. They also get speed at level 7.
Race doesn't matter as much, but dwarves are a good choice for valkyries, because they have good stats for fighting and most inhabitants of the gnomish mines will be peaceful towards you (so you can go shopping without endangering your life - as much).