A question about logic level shifting, 74LVC74, and 74HC(T) vs 74AHC(T)

[wraper]

To discuss datasheet values you better use the datasheet of the mentioned device and not some generic other one from a different part even if it's from the same family.

LOL, How should I use datasheet of mentioned device if you gave non existing model? , even series are not right, LVC vs VHC  . M74LVC1GT50 (non existing) and MC74VHC1GT50 (in the datasheet provided by you) is not the same 
Talking about particularly MC74VHC1GT50, input voltage thresholds are comparable (a bit lower) to HCT series at 5V, therefore good for 3.3V->5V. However they are significantly lower at 3.3V Vcc, 0.5Vcc * 3.3V = 1.65V max. Therefore they are not good at all for 5V->3.3V level shifting if you do care about noise immunity a tiny bit.

Edit:
BTW these are family related input thresholds indeed  , not particular part 1GT50 part. Here you go: MC74VHC125 http://www.onsemi.com/pub_link/Collateral/MC74VHC125-D.PDF or MC74VHC74 http://www.onsemi.com/pub_link/Collateral/MC74VHC74-D.PDF

[kjs]

yikes, I just recognized that I gave the wrong link. Looks like the 74LVC1GT50 is no longer available but the 74VHC1GT50 looks like it has the exact same specs (just compared with the old datasheet)..

[wraper]

It was actually sold as M74LVC first and ON had a lot of different but similar names for it. Lately they added the C to make it MC74LVC but we still have it under the old name in the database.
One issue with that part is that it's only available from ON and Leshan Radio Company. The closest TI part has different specs and can only be used in one direction (closer to the MC74VHC1GT50).

Then why you mention it at all if it is not sold anywhere? BTW even google don't know about such part existing. IMO you do have part number inputted wrong the database: https://www.google.lv/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=M74LVC1GT50

[kjs]

our database really needed a brush up.... They still had it under the pre-historic name. Sorry for that.
Just as a side note: the part TI cross references it to, SN74AUP1T50, only works for supplies lower than 5V (max 4.6V rating) and is not suited as a 3.3V to 5V shifter.

Funny thing is the m74vhc1gt50 name still exists.

[moffy]

Going from 3.3v -> 5v I would be tempted to use just a 74HC14, 74AHC14 etc as it will successfully trigger from a 3.3v CMOS digital signal.

Yeah, successfully, most of the times... Decrease 3.3V by few hundreds mV and it will stop to work, especially at wider temperature range or if unlucky with particular IC exemplar. Why do you think xxT series were created? TTL actually puts out more voltage than 3.3V.

For few MHz HC(T) series are fine. Most of the ACT series ICs work up to 100 MHz or even more.

Must agree, I hadn't noticed before how high the threshold could go on the "HC" parts: 3.15v max, ouch.
The 2.1v max of the "HCT" makes much more sense.