I've forgotten what you told me was the overall gallonage of the tank. Size could play a factor in your decision. Ultimately though, bottom or back, we can drill either, so no worries there. I don't think there's a substantial difference if you go with the back versus the bottom. In this case, one is going to be quicker to do than the other. But don't worry about that, once the job is done, it's done, so I guess it's just a case of whatever you think will suit you better.
From the 1/4" I assume the tank is not all that large, maybe 20-30 gallons or thereabouts. On that size of tank I'm not sure I'd be too worried about flow restriction, we're going to go with 1" bulkhead so we're not talking about 2000gph here.
If you think about how a durso standpipe works, you could build a cup style overflow drilling out the back, have the drain external to the tank, all that you have inside the tank is the 90 degree elbow. This is a keen way to do things. I'd draw up a diagram and post it but it would take me too long. Instead I'll see if I can find an example online already of what I'm talking about. The advantage of this would be the quietness of the durso without the invasiveness of the large standing pipe inside the tank, and you could have access to the whole bottom footprint of the tank for aquascaping (ie., no notched corner, which sometimes can be a pain).
If you were to drill out the bottom and go with the notched corner overflow, it would be pretty easy. You couldn't go with a Durso though. If noise was an issue you'd need to go with a Stockman style overflow. They work plenty fine.
That said, I have a 20g with the notched corner overflow and I just use a standing pipe with a strainer (no Durso or Stockman on my 20 although I use a Stockman on my 90). Because the level drop is not very much the gurgle sound is pretty much not noticeable anyhow. So this could all be a moot discussion.
I guess it depends on how tricky you want to get. 1/2" glass is a lot harder to break than 1/4" (although there are never any guarantees when you drill). But I've broken 1/4" a few times now (once I overtightened a bulkhead ... snap. Another time I was trying to wrestle some plumbing into an awkward spot, and I bumped the bulkhead, and snap. Another time I was wiggling some hose off one of those hose barb things and the wiggling snapped the glass - hole was too close to an edge I guess). That's about 3 times out of .. hmm I've probably drilled 1/4" about 20 times. So the failure rate is .. um .. sort of low
but definitely not zero. I haven't yet broken 1/2" glass (but there's a first time for everything!!!). Not trying to scare you here, mind you, just thought I should mention that drilling glass isn't completely risk-free. "Most" of the time it's fine.