As per the title.
What would be the easiest to play?
I think that there will be a lot a personal preference involved in any answer you get. Play style will have a big impact on what works best for you.
I haven't played all of the classes in ME3 yet, but I would suggest Infiltrator. They have really good damage output, and tactical cloak is very useful.
You can engage enemies from far range, which favors you. Cloak can get you out of tough spots and away from dangerous melee based enemies. The Incinerate ability is not quite as useful in ME3 as in ME2, but is still a good all-around tech power.
You will need to use party members that give access to Warp and Overload to make sure you can handle all enemies effectively.
If you do not have preference (i.e. you do not prefer to shoot a lot for example) - I would suggest going Sentinel. For me personally this is THE best single player class in the game (Mass Effect 2 included). You get both Overload and Wrap (important for taking down shield & barrier), Tech Armor for defense (really important, especially in ME2), and then finally - Throw (hello my auto-targeting weapon replacement).
Once you have all 4 setup and both Javik (DLC required) and Liara are in your team it's extremely easy to play:
With Javik & Liara reduce cooldown abilities + upgrading your own abilities with cooldown reduction, you'll get to the point where you can Throw almost every second... and you'll mostly use that to detonate opponents which you previously lift with Liara's Singulary / Javik's Pull.
You may run into two problems: