When connecting various 3.3V things (e.g., RPi, sensors) to and from various 5V things (e.g., Arduino, sensors), the following seems to be reasonable from what I've read:
5V logic -> 3.3V logic, use 74LVC245 (this seems to be the most widely used way)
3.3V logic -> 5V logic, use 74(A)HC(T)245. This is where I'm stumped. To TTL or not to TTL? What about AHC(T) vs HC(T)... any practical difference? I'm ordering parts and I have a choice of any of these (in DIP form), and the prices are the same or less for the A-type chips... was thinking of stocking up on a few each of the 74AHC245 and 74AHCT245 chips but if HC(T) is somehow better I would like to know because at some point it'll matter.
Bonus: is the 74AHCT125 just effectively a 74AHCT245 with only half the lines? The titles of the data sheets are throwing me off.
Note: Have tried TXB0108 devices for things. Not terribly effective and they are extra sensitive to... everything. Open the fridge? It acts up. Earth rotates on its axis? Don't expect it to work right.