I have invested in a lot of Belgium Pro League players (I will play with them for a few week until their price raises and then sell them on).
I also have bought a Korean Bronze team, some of the players ingame stats are very good. Especially with the 5* skiller Zicu it will encourage people to try and make a K-League team because of the variety of players. I also remember back in FIFA11 and FIFA12 the amount of Korean teams I came across in online single matches were ridiculous.
I haven't and I think I've made a mistake in not investing in some of the players in the Saudi League due to the fact that Jobson has returned and they have a couple of 5* skillers so it looks a lot of fun.
Single players to take notice of:
Silvers;
Ilori, CB, Portugal, Liverpool
Pisano, RB, Italy, Cagliari
Odjida-Ofoe, CM, Belgium, Club Brugge
Hugo Vieira, ST, Portugal, SC Braga
Golds;
Vidal, CM, Chile, Juventus
Fellaini, CM, Belgium, Manchester United
Reus, LM, Germany, Bor. Dortmund
Andre Schurrle, LW/LM?, Germany, Chelsea
Kaboul, CB, France, Spurs
Sakho, CB, France, Liverpool
There are going to be many players from all leagues to invest in, card weight will possibly determine how the price will be but if they have good 'crucial' stats such as, pace & strength the players will most likely raise in price.
If anyone packs high-profile players such as Ronaldo, Messi, Neymar or Ibrahimovic wait untill a few weeks after where people have a influx of coins and the market is a little bit more stable. I would recommend selling before January (Team of the Year) as a few could get some TOTY cards which will decrease the value of many (plus people will be spamming the pack store during the Christmas Period).
Always research your players price as well before selling as the market will be changing constantly.