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I use Time Master +Billing for tracking my clients and it allows me to sync from my iPhone to my iPad. When I invoice my clients, it has an invoicing module (which can be modified with your own logo) to create pdf's and it also exports to Quickbooks format if needed. I can creat jobs as time entries or as expense entries. I can over ride the cost per client as I charge different rates depending on who my client is.
As for ios vs android, you use the tools that work for the platform you use. I have both large enterprise clients and small mom and pop organizations.
Hth.