Thank you for contacting us. You are asking a question that truly you are the only one that can answer. Every tank is different and flow is INCREDIBLY subjective. What may seem like good flow to someone may be too much or too little to the next person. At the end of the day, you and your tank are the only ones that can tell what works for you. I personally like my pumps horizontally on opposite ends instead of vertically but again, since flow is very subjective, it is a matter of preference.
My suggestion is for you to try it multiple ways and see which way you like best. Which way gives you the best flow and covers all the corners based on your aquascaping.