Which one is it?

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I don't shop there so cannot give specific advice, but I'd bet something with "chianti" or "Rioja" written on the label. In the 6-9 Chf range is decent enough with broad appeal and goes with most foods. Anything cheaper than that is very much in the table wine range, which can be completely fine, but almost certainly won't impress (else they'd sell it for more!) and is likely to be more acidic or tannic which complicates food pairings.

Hope this helps, please report back with your findings

I recently bought a 2011 Bordeaux for about Euros 3, which was excellent.

Can't say for Lidl, but I buy a 3l wine box (bag-in-a-box) from Aldi - Italian Syrah - for less than than 8 chufs (approx 2,65/l).
Quality is good table wine standard and 2 other varieties are available.

I'm sure Lidl have similar.

Wine boxes are preferable to bottles (if not drunk in one go), as there is no air in the bag, and none enters as wine comes out.

You one you enjoy most at the price you want to pay.

Too many to choose from, really, but if I were to choose one for outstanding value it would probably be their Tarragona Gran Reserva, variously priced from EU2.99 in Germany to a rip-off chf7.99 (normally, but occasionally on offer at half prince 3.99) in CH. (Guess where I buy it?).

It's a really good rounded wine, a tempranillo/cab sav blend, oak-aged for five years, IIRC. Could easily be mistaken for a very good Rioja and would probably be priced three or four times higher if it were.

I would like to recommend you a cheap good wine which was recommended to me recently. I have to agree, top for the money.

Castillo Hermmoso at Denner. I think it is 5 or 6 CHF for a bottle.

Let me know what you think if you try it.

The cheapest one per litre?

No, the one with the highest metric-yum per rappen coefficient.