I also have only positive experiences with NKON.NL. I just received a batch of unprotected 21700 cells very cheaply:
To get cells with high capacity, just move the slider “Typ. capacity - mAh” to the right, e.g. to 5000mAh.
I bought with Samsung INR21700-50G (cheaper) and LG INR21700-M58T (higher capacity), both with clear wrap (“reclaimed” from an automobile project).
You can disregard the bad review for the LG cell, the reviewer is kind of clueless…
You can find / compare cells in this table - the headers can be used to filter (e.g. by size - 21700) and sort (e.g. by energy - mWh @10A):
https://lygte-info.dk/info/batteryIndex.html
This page allows a 1-on-1 comparison (the LG M58T wasn’t tested yet):
https://lygte-info.dk/review/batteries2012/Common18650comparator.php
Another comparison table, from Mooch:
The Samsung cell is in the top ten for 3A and 10A discharge:
https://lygte-info.dk/review/batteries2012/Samsung%20INR21700-50G%205000mAh%20(Green)%20UK.html
The LG cell was discussed here in BLF:
DON’T by the cells WITHOUT wrap if you won’t wrap them yourself - the outside is not electrically isolated, and you could
easily short-circuit the battery, which would be a real problem with this battery size (both total energy and max. current).
If you want a protected cell, the Sofirn 21700 5000mAh are nice - I bought some directly from Sofirn. A test:
https://lygte-info.dk/review/batteries2012/Sofirn%2021700%205000mAh%20(Black)%20UK.html
Here you can read reviews of chargers:
https://lygte-info.dk/info/roundCellChargerIndex%20UK.html
I bought several Xtar SC2 chargers, because they are both cheap and fast (1x 3A or 2x 2A). A review:
https://lygte-info.dk/review/Review%20Charger%20Xtar%20SC2%20UK.html
I could also buy them at NKON.NL, but now they are out of stock:
If you get the Xtar SC2, you need a USB charger with 12V PD (PowerDelivery) - otherwise it will charge with 1x 2A and 2x 1A.
Unfortunately, the 12V option was made “volontary” in later versions for USB charger standards, so some chargers support it, some don’t.
I bought the XTAR PD20W, which supports 12V: