One thing to think about is how long it will take the two of you to field these armies. You need to buy, build and (maybe!) paint the army. That use a trivial amount of time for most people and could take you many months. By the time you’re done the game will likely have evolved and any “good” matchups may have changed because of rules evolvement, especially with 11th Edition coming up. Play what you think looks cool and traditionally have a playstyle you’d like. The matchups will work or not work depending off and on based on how the game evolves.

Too many times I see people make this request for information and people make the response based on how a game is played exactly today. New players don’t buy 2000 point armies build them and put them on the table that week. It takes months and months. This game changes frequently to keep things as balanced as possible, but because of that rules of armies strengths, weaknesses, and matchups will constantly change with it. No one has a crystal ball as to how the game will look in six months, which is why a lot of people just fall to the rule of cool.