Depends what your normal shopping list is like, I think.
I'm in the same situation as you'll be in - modest sized LIDL closer than modest sized Aldi. I pop into Aldi when I'm up by them for any reason but LIDL I use all the time - in addition to Sainsbury's Home Delivery for the heavier stuff.
On a limited sample, I've found LIDL's prices to be very slightly higher than Aldi's but their quality to be a lot better on things like Cooked Meats and Delicatessen (look out for the Dulano brand) dairy produce (look out for the Milbona brand) and their tinned and bottled goods. Much of their produce is from the continent and it's generally excellent value and quality.
They don't have the range of goods that another supermarket might have but there are also some things I go to them specifically to buy, and not just because they're cheaper eg
Red grapes - I don't know who their buyer is but they should get a medal
Cottage Cheese - Best on the market - and dirt cheap
Cream cheese with garlic and herbs - ditto
Mister Choc Chocolate Raisins - cheap and a great quick nibble when you feel like chocolate (just a handful will satisfy the craving)
Dulano pepper salami (and other Dulano and continental cooked meats)
Clumping Cat Litter
Personal care
Ice Cream
Vegetables and fruit as needed - I've found them to be fine
and so on.
I'd be a bit careful, though, with household laundry and cleaning goods etc. I've not found them to be good value at all. I've never tried their raw meats.
All you can do, really, is go there and have a mooch round. As always in a new place just buy one or two of things so that you can test them at home. It won't amount to much anyway.
(They have weekend specials so best to go there on a Saturday if possible.)