I suggest-
1. Make a list of everything you might ever need, e.g. track saw? gardening tools as well? Then ask yourself, does the manufacturer have all these?
2. I know of 3 battery systems that work across manufacturers.
2a. Bosch 'Power for all' 18v (considered domestic)
2b. Bosch 'AmpShare' 18v (considered professional)
2c. Metabo (release button is on tool which makes them awkward to detatch)
The other manafacturers using these battery platforms tend to make specialist tools so this may not be a benefit for you. Although Fein might be worth considering for their Multitool ... which they invented.
3. Some battery systems are higher voltage, e.g. Flex, which will provide more 'grunt' if you need it. Makita cleverly have two 18v batteries in series on their Track/Plunge saw making it 36v. Some DeWalt tools and batteries can operate at 18v or 54v but note an 18v only battery will not power a 54v tool.
4. Some manufacturers have 5 year warrenties e.g. Flex and Hikoki.
5. Toolboxes are worth some thought. Manufacturers supplying their tools in Tanos Systainers include Festool, Fein, Metabo, Mirka, Mafell, Lamello, Sthil, UJK-Axminster. Bosch and Flex supply in Sortimo L-BOXX. Flex and Milwaukee are leading the field with rolling boxes and toolboxes with drawers instead of lids catching up with what car mechanics and kitchen designers have been doing for years.
6. Thieves are attracted to big name brands Bosch, DeWalt, Makita, Milwaukee etc. Lesser known brands might be less attractive.
7. Cost - if you are starting out do you need big names? How about Parkside from Lidl - super cheap, and if they don't last, you have not lost much if you have to replace them.
Hope this heps.