I've used both xero and freeagent for my own businesses and as an accountant have used lots of big company accountibg systems also. Never actually used quickbooks myself but every comparison I've read is that xero is far more usable.
I can strongly recommend either of these two, although for your purposes freeagent would be more suitable. xero is more fully featured and will scale for large companies, and cover all kinds of business models eg carrying stock etc. Freeagent is designed specifically for small services businesses like consultants and contractors, is very easy to use and has everything you need built it. For example it can automatically import and reconcile your bank statements, prepare estimates, track time and vehicle mileage, run payroll and prepare & submit taxes. Also has good mobile apps.
I can't see the prices on US website as it takes me back to UK site, but here in UK it's £30 per month. Many accountants also provide it for free as part of their package which is how I get mine, and I don't pay any more than I would have for an accountant who just gave me a spreadsheet to fill. So it could well cost you nothing assuming you would have a cpa for your business.
Happy to answer any questions