Best approach to buying tools?

I have mostly Craftsman, with the exception of some specialized individual tools from Snap on.
Snap on has a real nice double box end long wrench with 6 point 8mm on one end and 10 on the other.
Now obviously the cars we are here about are all good old American standard sizes, but 8mm crosses to 5/16 which are usually in places a long wrench works best. (for breaking them loose without trashing the head)

Another is a 1/4 drive speed handle with swivel sockets, and one more is a 36 inch 1/2 drive to 3/8 drive extension and 3/8 flex drive impact sockets. (Makes bell housing bolts a total breeze.)

There are situations where mixing specific metric tools with American can come in handy, like the 8mm wrench or socket fitting 5/16 nuts and bolts.
Or a 14mm box wrench on a 9/16 bolt head because it fits tighter on the bolt than the 9/16 and has less chance of slipping off.