Obviously you are referring to league standard.
Therefore, I would suggest you want your most consistent batsman opening, usually players who are in form and hitting the ball well, then support the inform players with players who can give them the strike and support them in the innings. I think what is hard in a batting line up is when you have a lot of out of form players or a weak batting line up. I think training session are useful to decide your batting line up, to see who is batting well. But I think a good captain can alter their batting line up depend on the game situation.
In opposition to this, our Sunday batting line up allows everyone to get a fair and to play a part in the game, for example, if players want to bat they can open the batting and try and get a knock, the bowlers and the wicket keeper goes in at 8, 9, 10 and 11. Obviously if any batsman have a poor game they can have a bowl as well.
Absolutely love @stevat 's method of opening with a tail ender to throw off the opening bowling attack.