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I’ve previously run a few businesses and I have tried a few of the accounting solutions out.
I’m not sure there is a best option - I really would suggest trying them all on a trial basis if possible or paying for a month’s worth and cancelling if it’s no good, to see which one will fit you and your business the best. I had to redo about 4 months of books when I went from QuickBooks to Xero so I would say its best to ensure you’re 100% happy with your chosing accounting platform before you jump in!
KashFlow - did not get on with this at all. Confusing, and expensive. Their staff kept contacting me to try and upsell stuff which while I appreciate is a common thing for me to do, is the fastest way to put me off a product.
QuickBooks - I used this for a while and found it was alright. Only weird issue I had was when I started having lots of transactions (high volume tight margin ebay business). It seemed to choke on more than about 50 per day, the interface would go weird, it would throw errors etc. Their support was quite slow. It does however have quite a few banking integrations that are free to use.
Xero - probably my preference. Moved my business over to this one and found it worked well for me. A bit more manual work to do though but they seem to intergrate with pretty much other platform.
Sage Accounting - not used this myself but Sage is a very, very big name for accounting in the UK at least. If you want to use a British designed and built solution, they might be a good contender.
FreeAgent - another one I’ve not used but seems well optimised towards small businesses. I believe if you bank through Natwest or RBS this is a freebie they include.
Hope this helps, sorry I don’t have an answer on which one is best but hopefully something in here will help you!