With the nerf of tp i think Ignite is an overall better pick than TP with that being said…
Lets first start with saying that IN MY OPINION this decision is mostly based around your elo and your personal preference (eg: in bronze even if you ping 5 times, most of the people will not notice you are tping). If you know you are NOT used to watch the map for opportunity i rather take ignite and try to win the lane with lol boost. If you are instead confident enough or for whatever reason you feel like you will either teleport botlane or need the tp back to lane feel free to take tp.
14.png You are confident enought in your ability to STOMP the enemy laner because you either know the matchup or for some reasons you think you are way better then the elo are you. As said previously take ignite if you are not used/confortable with tp
12.png You are the playmaker and you know exactly how to maximize the values of your teleports. Take this spell if you are used to watch the map or if you are in an uncofortable matchup (eg: lulu, darius). Make sure to remember 2 things:
-If you need to tp back to the lane, USE IT ALWAYS on your turret because it will reduce his cooldown
-You will lose a considerable amount of your kill potential in lane
Also teleport is usefull for lategame splitpush, but i feel like in low elo unless you are carrying hard people will not listen to you and they will get caught 4v5.
4.png Provide you the ability to make PLAYS. Even if you are not supposed to be the engager, if your team does not react fast enough at a certain situation, well… with flash you CAN make plays (ex You see an enemy carry alone, fairly away from other enemys but your Q is not enought to catch him, well just flash Q and melt him. I won so many games by doing this, while also sometimes i failed because i got coocky and went too deep)
6.png If you feel brave enough, i would not take ghost over flash. Most of the time you need to you your Q to engage and also your q is not instant it has a cast time, and you can be catched by a CC while mid-air-jumping so, well.. i feel like your q is not enough as escape.
3.png It can be a good choise vs certain champions if your support is running ignite. Let’s say you are vs an ap kennen and you have no exaust in your team. In this case as soon as kenne ult you will use your exaust on him and negate him most of the damage. Anyways this is more a team oriented summoner choise and a really niche pick.