1-4 gives 169 EXP (deploy 3 allies) and the cooldown has remained only 1 minute, so in theory you could get 845 EXP from it every 5 minutes. However, when I tried completing the mission as fast as possible, it still took me a few seconds longer than 1 minute and more importantly, you get Mina popping up a message 3 times during the quest! This makes grinding in 1-4 so much more annoying than doing a normal 5 minute quest, so I don't recommend doing it.
Instead, do 38-6. It gives most EXP of all 5 minute quests (660 EXP) and lets you deploy 5 allies, so you'll be racking up ally points too. The mission is easy enough, with only ground monsters that resist missile: Orthros, Scarecrow and a few Hydra.