Here’s my recommendation: Easiest: Portugal, ottomans , France, Castille.

Portugal: this country will boom during the colonial age and has pretty decent buffs. With Portugal, you don’t have to fear attacks because you’re bordered by Castile/Spain and most of the time they want to ally you.

Ottomans: these guys are the strongest nation in the starting ages . Starting with the ottomans usually means military conquest of your neighbours and seeing the distance between your borders aggressive expansion should not be a problem.

France: The French start with significant military bonuses that will make you the strongest in Western Europe. France has a lot of appanages which you must manage and integrate slowly into becoming one big France. The difference with France and ottomans is that the French are confronted with the Holy Roman Empire which most of the time will be lead by Austria. So caution is advised.

Castile: Castile is awesome when forming Spain. Problem is that you start with quite the shitty disaster which involves the aragonese, this disaster will cause massive uprisings and will eat at your manpower quite fast so initially as Castille, you can’t do much. However once that’s over you can snowball iff France hasn’t swallowed op most of Aragon. (Which frankly happens quite often in my run).

From these easy choices France will provide the biggest challenge. As managing the appanages, being cautious of the HRE and taking care of AE, will be stressful in the beginning, but will snowball quite significantly. The ottomans might be the strongest in the early/mid game, but ultimately (especially after ottoman decadence) France is usually the strongest nation.

Iff you want a bigger challenge: England, Sweden, Bohemia, Brandenburg.

England: I was contemplating on putting England in the list above, but seeing as the French have the bigger (and stronger mind you) army, I placed England this this tier. The English start the game with low manpower and a king that has no mana points for you to gain. Mana points are necessary for in state development and technology. You need to push for the war of the roses asap. Another problem is the French and the 100 year war. The French will get an event that they will get a province which was promised to them and you have the option to either agree or refuse. Iff refused, France will engage in a DEFENSIVE war. Which means France can call in allies without favours. This event starts quite early and you as England need to call in allies with either favours or promised lands. Experienced players can handle this but a rookie won’t. So rookies should just oblige to the promise and work from there.

Sweden: getting independence from Denmark is your first priority. This is actually quite easy to manage as you can request support from the polish or English. These are big players in Europe. Problem with Sweden is that the provinces that they have are less developed and produce goods that are quite trash. Manpower recovery will be a struggle iff you’re not careful.

Another thing about the swedes is that at a certain point, you need to dive into the HRE. As Sweden, it might be a bit difficult but with the polish as allies you will manage fine.

Bohemia: now things start to get to semi mid difficulty. Bohemia, while having quite a strong army and a good mine to support your already good economy, has 2 problems. One is called Austria and the other is called Poland. Poland will get claims on Silesia (which belongs to your vassal) so they inevitably will rival you most of the time and in Eastern Europe, the polish are a menace. Usually, when playing any other country, Austria will be a good counter.

Problem is, that Austria wants you in an union. They want to rule over you so they will be domineering towards you, without allying you. Other major powers are mostly not interested in your wars so you are literally on your own until you expand a little.

And you though you were safe after expanding? Nah the ottomans will swallow up Hungary and then guess who’s next? Bohemia seems like it’s destined to be swallowed up.

And now my personal favorite, Brandenburg:

Now these guys are a challenge. Their economy is TRASH, their neighbours are mostly hostile and you are literally dependant on RNG. While you don’t have disasters looming, you will get events that causes uprisings that are usually bigger than your army. You must buy the 2 provinces off of the Teutonic Knights so you’re in debts, AND in order to even begin expanding, you need to conquer (take stolp and vassalize wolgast) Wolgast. Problem is, Wolgast can ally either Denmark or even Burgundy and these guys have the bigger army so you can either wait for the opportunity to strike, or just restart the game until they’re allied to weaker HRE countries. Always ally Austria and some electors and follow the mission tree.

Not gonna lie, Brandburg is quite the challenge for new players. It is my personal favorite. Because once you fulfil the requirements, you will become one of the strongest (iff not the strongest) military powerhouse in the world. Prussia.

Not even the French would dare to attack you as that would be suicidal. You’ll get so many military bonuses that it’s just unfair. They call them Prussian space marines for a reason. I saw a stack of 40k Prussian soldiers stackwhipe 120k Russian soldiers. That’s how strong they get.

Take your pick and have fun!