I'm updating my gear and I'm curious about which multi-effects pedal to get out of these 2:

1.Zoom GFX-8

2. Vox Tonelab ST

I'm leaning towards #2, but I don't know.
Between the two I would get the ST. But I would get a Boss ME-25 or an RP355 over the ST. And the Zoom G3 over any of them. However the G3 is a different kind of multifx so it depends on what you feel you need.
I'm looking for a blues-rock or old school hard rock multi-effect pedal.
Are you interested in a drum machine and/or looper?

Boss ME-25 - 38 sec looper, no drums.
RP355 - 20 sec looper, drums (looper cannot be with drums)
Zoom G3 - 40 sec looper, drums (drums sync to looper)
ST - No looper or drums

All can do blues/hard rock. Zoom G3 doesn't have an expression/vol pedal and acts as 3 individual pedals built includes amps and cabinets. An external vol pedal can be purchased for $30, but still lacks the functionality of a built in exp pedal.

In my profile Sneaky and Unsynced Jam are the ME-25. Some Bird, Baldwin Park, Orange Chimera, and Outta Town are the Zoom G3. Jelly Jam uses both the G3 and the ME-25 together.

The ME-25 is unique in that it has a cool freeze effect (like the EHX Freeze pedal). So that and the 38 sec looper make it worth considering. The user interface is pretty spartan and lacks footswitch. It's really like the ST except it has the looper and freeze.

The RP355 is good all around, has more footswitches and a nice computer preset editor. The amp models and effects are solid.

Despite the G3's pedal style design lacking the exp pedal and a longer string of FX... IMO it has the best combination FX and amp models of any of them. And having the drum machine synced to the looper is unique to the G3 among all multifx. Nearly every song in my link is done with a looper.
I have too many drum machines already and I'm going to get a looper after buying this pedal.
Your drum machine won't work very well with your looper. Even if you can be very accurate with setting the loop it will get further out of sync with the drum machine every loop.