>>1671189Play 6 (Embodiment of Scarlet Devil) first which is what the majority of people start with as the first non-PC-98 game, or failing that 10 (Mountain of Faith), which is generally considered a well-balanced game that is typical of the Touhou experience, with no outstanding gimmick mechanics. For the "best", the polls themselves seem to point at 8 (Imperishable Night), though I don't really get what's special about it myself.
Touhou 2 (Story of the Eastern Wonderland) is the first shooter game in the series, but it's also very hard. Like, giant hitbox and tiny hard to see bullets and no focus (hold shift in Windows+ games for focus, it's a real life-saver!) hard. It has one of the hardest extra bosses in the series, being so hard. Only play if you have experience in shmup games. Good luck and have fun! It's been a while since I last played, but the newest Touhou game, Hidden Star in four seasons is coming out in 9 days!