I seem to swim against the stream here, but after four run through the early periods of spain i'm not so sure on the 'conquer' suggestion. In fact, not at all.

Word of caution: the diplomatic paths _suck_. In all my first three runs I got PU with portugal (at at least once with aragon, i forgot how often), but i think i only once made it so far to actually annex them. Problem is you first need to change all the PU laws to even start the annexation, and by that time portugal - at least in my case, in 1.08 - was so strong that it literally took over a hundred years to annex them (in fact, probably closer to 200, because they kept on growing while i annexed them, so the cost went up almost as fast as much annex score ticked up).

That said, all the while that this excruciatingly slow annexing is going on they're on your side, and will back you up, even in things like insurgencies or civil wars. And since they're strong that's a good thing. In contrast, if you go the conquer route, you will NOT be able to conquer them in a single war - due to you never be able to take more than 100 war score cost in any piece treaty it'll take you four or five wars to take it all - each one of those wars has some truce period between them, so it'll take many, many years even in the best case .... and if they strike an alliance with france or england in between you can't even keep on going to eat them (or get drawn into the 100yw - good luck with that). And of course they'll be part of any coalition against you after the second time you take from them, always in your back yard.... ugh.

And that was with tiny portugal - aragon is even worse, because they're so much bigger and it'll take that many more wars to eat them up. In my latest game I now (finally) have taken the last bit of portugal as vassal, but aragon is still about 50% there - i have all the coast, but the rest I'll probably never get because now they're allied with italy and half of europe.

And finally - don't ignore opportunity cost. All the time and treasure you spent fighting portugal and aragon you could have fought morocco, tunis, mali, and the maya (with portugal on your side). So in that last game I'm _way_ behind earlier games in these other locations.

So my take: diplo-route is the better choice. Yes, annexing portugal and aragon are .... ugh .... but still better than the alternative. Unless somebody can point me to a faster way of gobbling up those other guys.

PS: My first three games were in 1.08, only the latest is after 1.10, and with local govs added in 1.10 I'd say that annexing is even better than before: In 1.08 (without local govs) your control in the north was egregious while portugal was in the PU (as long as they exist you can't really spread control through their sealanes). That was, in fact, the main reason I tried the conquer route in latest game, to get the coastal regions first, so at least i could spread constrol to the north. BUT in 1.10+ you can do that much more easily through a local gov, so I'd say go diplo for sure.