Thank you for posting this! I'm new to Splinterlands myself and enjoy reading about the experiences of other new players.
For my low-mana matches (assuming the standard ruleset), I usually use the Fire splinter, with Malric Inferno or Pyre as my summoner. I don't have a suggestion for a Death team at very low mana levels (12-15 mana limit).
Some general advice I try to follow is to avoid focusing too much on the daily quest while composing teams. I just pick what I think is best based on the mana limit, ruleset, and opponent's history; and I eventually complete my daily quest through the natural course of play. Yes, it probably takes longer to complete the quest, but I come out ahead overall because I'm getting more DEC from wins, and I'm not burning through my Energy Capture Rate (ECR) as quickly in the process. Especially lately, it seems like the Daily Quest chest rewards aren't worth sacrificing one's win rate for.
Thank you so much for the suggestions. I should start pay less attention to daily quests as well. Fire quests are normally easy to complete. It seemed Fire is more newb friendly.