I recommend Silverstack software if you have more than couple of shooting days. better verifying options and much easier to manage larger amounts of cards in the library.
you will want to check for having the right connectors in the laptop and the required amount of them. the newest macbook models will need adapters to work with the card readers and to get reasonable amount of connectors so you will need to take that into account.
windows laptops are ok if you don't need Silverstack (shotput pro is pretty much the best you can do on Windows) and you will check very carefully that the connectors are right for you (they may for example have usb-c connectors without thunderbolt3 circuitry and so on) .
on windows you will get more processing power on the same budget, especially GPU's will be much more powerful for the price, so if you do proxies at the same time on the same laptop it may be beneficial to have a Windows laptop, for example one made originally for heavier gaming use.
you probably don't need Retina displays for simple offload and management tasks and the laptop displays are generally too small for quality control work anyway so they are no reason to purchase a mac, concentrate on other aspects instead.
both Windows and Mac are a tad unreliable so you will need to know your system well and DON'T DO ANYTHING ELSE with it during the gig so that you know you/someone else did't update software X which made data management software Y nonworking in the middle of the shoot etc. . Or a trainee using it for shady personal business when offloading cards and downloading and installing all kind of crap to it
Personally I like to not even have the DIT computer connected to the internet most of the time when on a shoot, only connect it if absolutely needing to upload dailies or something other dit related.
the computers will be your worst nightmare on set, they never work correctly all the time so be prepared and don't trust ANY system no matter the brand