Are masters programs generally easier to get into than PhD?

Not every STEM Master's program is going to be easier to get into than every PhD program, but on the whole they are easier. Universities are much more likely to take you if you're paying your own way (aka. a Masters) than if they have to fund you. In the US it's common for students who didn't do so well in undergrad or are from a lesser known international school to pay their way through a Masters first and then go on to a PhD after proving their worth.

That being said, do not discount how helpful research can be. A published paper or a good letter of recommendation from a known professor can go a long way to erasing some bad grades. What counts in a PhD program is your ability to do research.

Generally, a master program is easier to get into than a PhD because:

• You pay for yourself
• You don't have to find a supervisor
• The university can deliver the same program to many students

That being said, from what I can see, you're very concerned about your academic grades. This is not a good indicator being a good phd student. Nobody cares how many A you have as a phd student, it's your ability to do research matters. Your grades won't matter ("look good" in your words), because every other phd student has the same grades.

Unless you are truly interested in research, you should just focus on master degrees.