Wrestling is definitely one to look into obviously. The clinch is where a fight can be very easily decided in the long run as it dictates where the fight goes. However, boxing as much as possible is worth it if you plan to become serious in the sport, because against another wrestler with superior ground game, you need to be able to finish him standing and keep the fight up. Vice versa, you need jiu jitsu to defend incase you need to bring the fight down against a better striker. All in all, given that everybody knows that a full game is needed.
The best 2 style base combo I think would be Wrestling and Boxing, just because you have ground and pound potential as well as the ability to stand on your feet. Wrestlers are usually, but not always a tad more difficult to submit due to their good base on the ground, no pun intended. However don't make them istake of standing incorrectly like someone else mentioned, which is often a mistake wrestlers make, which is leading too much with the lead foot, putting their weight on it and making themselves vulnerable to strikes.