I am going to add a couple of facts I figured out while recording:

For this particular category, it is all about 2 factors: Efficiency of special rooms and specimen difficulty. Efficiency of special rooms is how quickly one can surpass the room(s) before the specimen gives chase. Specimen difficulty is self explanatory.

Example: Spec 12 case is easy, but its room takes too long to deal with. The specimen would be on the no encounter list because of its efficiency of special room.

With this info, I composed a list of specimen you want to have in a game:

M3 (room is a simple square. And he rarely blocks your path) M2 (Forces you to be quick, which is exactly what a speedrun is about!) S7 (One time, and the special room + chase sequence takes up literally half of a set (1 set = 100 rooms)) S3 (Same reason as monster 2) S5 (Tanky, but too slow to pose a threat. Rooms are average length but it is 4 rooms prior to chase) S6 (This one is questionable. It can corner-cut and lay a hit, but you can hit it immediately after and regen before enterance to next room) M4 (Same as above, but less damage. Plus, REEEEE) M5 (This cow is more helpful than harmful. If comboed with a phaser such as Spec 4 or 8, it makes your life a whole lot easier!) U2 (Need I say more?)

And a list of those you don't want:

S12 (mansion takes too long) S13 (The mechanics of the chase make the chase long) U5 (need I say more?!) U3 (puking takes up time) S11 (Restaurant takes too long) S10 (Too fast? Swerve time!) S4 (both types. Rooms are fine, but phasing will play a problem) S8 (same as above. Plus you can actually die in his special room if you aren't careful.) M6 (although a chance encounter, still time consuming to backtrack but risky to tank damage) U1 (LET'S TAKE OUR PRECIOUS TIME TO LISTEN TO BREATHING!!!) U4 (Let's use up our precious stamina to whack some imaginary animals)