According to PCBshopper JLCPCB would make 3x 2 layer 10cm*10cm boards for 31.59€ and delivery in 7 days, while Aisler would make them for 37.20€ (with delivery often within 3 business days). In my experience there's often a 20€-ish customs charge and sometimes additional delays when receiving packages outside the EU, so in the end Aisler ended up being cheaper in my case.
* JLCPCB Green 5 €1.86 total €0.37 each (Minimum order qty 5)
* AISLER Green 3 €37.20 total €12.40 each
Even with shipping & customs (20EUR extra only for JLC), AISLER is still 76% (1.76x) more expensive. Now I do see that for some reason AISLER's shipping is more expensive which is dumb because it's significantly less distance, but it seems like I can't replicate your JLCPCB data; did you further customize it?
32EUR from JLCPCB for priority 7d and 26EUR for standard 7d (not sure what the difference is to be honest). The claimed price from AISLER is 57EUR. Although I have ordered from JLC before I don't have any receipts (and usually can afford slow shipping); to BE/NL/LU/DE it is generally delivered within the claimed timeframe (although 2 working days deliver is not an option).
> Actual example from a 33x55mm board
For 3x 33x55mm it does seem like AISLER comes out on top, probably because they charge by the cm^2, although in the higher order quantities that scaling makes it quite expensive.
I think the price per cm^2 of AISLER is about 5-28x JLC (JLC doesn't charge by cm^2 for <100cm^2, so a lot of variance; for larger boards it's back to about 5x). The shipping costs is (for me) about 0.5x, so when when your cm^2 is high (which for us it often is) it can be more expensive. Also something to note is that the JLC price per board decreases as you go to higher order qty, about x/|_log2(n)_|.
So my takeaway is that for <100cm^2 & >2000mm^2 and medium-high order qty JLC will probably give significant savings, at <2000mm^2 AISLER & <10 boards costs about the same as JLC everything considered (if your shipping costs is lower it will probably be at a higher mm^2 cut-off).
