From: San Diego
I have very similar patrol patterns: tight 3-hex triangle patterns where possible, or 3 in a row in areas like Malay Straits. I try to avoid single hex patrol patterns because they tend to get an ASW TF sitting on the same hex pretty quickly. In larger deep-sea areas, where I'm not sure of exact shipping lanes, I will use a larger triangle pattern with an empty hex between each patrol hex. I put ones like this in the areas south and southwest of Japan, or off the US West Coast and PH when playing as the IJN (which I pretty much never do).
As for specific locations, you really have experience playing both sides to really learn where the shipping lanes lie. Some players have the exact hexes that ships travel from SF to PH for example (and other common auto-convoy lanes) and flood them with subs. As a predominantly Allied player, I tend to run into a lot of IJN Subs in the lane between Cape Town and Perth, the NW corner of Oz (off Exmouth), between PH and the USWestCoast, off the southern tip of India near Cochin and Trivandrum, between Karachi and the Abadan exit point. These are all well travelled by AutoConvoys and thus are active hunting grounds. With my subs, I throw a lot around Japan of course, particularly near the exits from Osaka and Tokyo, and the lanes around Hokkaido and that northernmost island they share with Russia. Early on (first 6 months), hexes north and south of Formosa are great, as is the southern and SE coast of Vietnam (Cam Rahn Bay to Saigon), and all the little chokepoints between the DEI islands as they begin to fall. Once fallen, I concentrate most of them outside of large Oil/Resource/Fuel bases in the DEI/Burma area like Palembang, Singapore, Tarakan, Balikpapan, Soerabaja, Rangoon, etc. Big forward bases usually get a few as well (Truk, Rabaul, etc)
I need to play more as Japan in order to get a good idea where their auto-convoys tend to travel.
Lastly, all the directionals I used in this post (NW, SE, etc) are map-based directions, not IRL-based compass directions.