I've worked with VA's hired directly through Elance/Upwork, a Zirtual assistant for about a year, TaskRabbits on occasion, as well as FancyHands. FancyHands has become my go-to VA service, having delegated over 1000 tasks to them to-date.
The most important question in my mind is why would I use your new, unproven service when there are already established options to choose from in the market? The existing options cover a wide range of service models and price points.
Here's how I currently see the market -
eLance/Upwork - Very hit or miss. You'll spend a lot of time finding and testing VA's until you find the right one. Once you do, you'll be hoping he/she sticks around, so you don't have to go through the selection process again. The benefit here is that eLance/Upwork assumes a lot of the risk from you when it comes to paying for work completed. This transfer of risk is the benefit I see from platforms like eLance.
Zirtual - Great for semi-dedicated and consistent assistance, especially important if your tasks require some historical knowledge. For example, I worked with my Zirtual VA to invoice clients on a regular basis and keep track of payments. Premium price point and premium service.
FancyHands - Fantastic one-off task completion, can assign multiple tasks at once, to get them done simultaneously. While you don't work with the same VA all the time, FancyHands has done a nice job ensuring that the quality of results is consistent across their team of VA's. Various price points and a high level of service. To me the highest value/cost ratio out of all the options in the market.
TaskRabbit - For things that need to be done in person. Their recent pricing model updates have made me begin to question the value provided vs. price paid. At least for me, as the service has gotten more expensive, I've begun to use fewer TaskRabbits.
Happy to discuss further on a call, if you'd like some assistance differentiating your service or identifying gaps in the current market landscape.