Should i invest in a Antminer L3+ or a Antminer S9
Invest? Run the math first on bitcoinwisdom.com. Unless you have free power (and won't get into trouble drawing a kW of AC 24/7; it won't be profitable for long. 

Difficulty rises and will continue to do so; until the correction comes; which- it will. 

Now would be a bad time to buy a miner. I would wait for a major price correction-- even if BTC hit 10k before the correction- the money to make would be after it drops back down to 5k and the miners are all worthless; then start them up after the price rebounds. 

Bitcoin mining is too hot to touch right now if you are not already heavily invested in the game.