In building a Magic: the Gathering deck, I usually aim to use a core card or card components and build a strategy around it. The problem then goes with the card’s consistency and the synergy with the deck build.

For example, a control deck archetype uses card draws to resupply its hand of counterspells, mass removal, and planeswalker support. If you are only considering winning via a planeswalker ultimate ability, then you need to also check the instances when that win route is hard to achieve. In that way, you can have options like attacking to reduce life totals to zero as an alternate.

When determining the best cards to use in your Magic: the Gathering main deck, consider the following factors:

1. Synergy: Look for cards that work well together and complement each other. For example, cards that share a creature type, a color, or a theme can work well together and create a cohesive strategy.
2. Power level: Choose cards that are powerful and effective for their mana cost. Look for cards that can provide a strong advantage, such as creatures with high power and toughness, spells that can remove the opponent’s creatures or draw you cards, and so on.
3. Mana curve: Make sure you have a balanced mana curve, meaning that you have enough cards that can be played at each stage of the game. This will help ensure that you have something to play on each turn and are not stuck with a hand full of unplayable cards.
4. Meta considerations: Consider the current metagame and the decks you are likely to face. Choose cards that are effective against popular decks and strategies, and avoid cards that are weak against them.
5. Your play style: Choose cards that fit your play style and preferences. For example, if you prefer an aggressive play style, choose creatures with haste and low mana cost. If you prefer a more controlling style, choose cards that can remove or neutralize your opponent’s threats.
6. Testing: Playtest your deck to determine which cards are effective and which ones are not. Make changes to your deck as needed based on your playtesting results.

Overall, the best cards to use in your main deck are those that fit well together, are powerful and effective, have a balanced mana curve, are effective against the current metagame, and fit your play style and preferences.