To start with, the technical differences:
Voyant Adviser can be used on, or offline (provided you have set up offline mode on your machine), so it can be used when you are not connected to the internet. Voyant Adviser requires Java, so this must be installed on your machine, which explains why Adviser will not run natively on iPads, and other tablets which are not Java-enabled.
AdviserGo is entirely web-based, so it will only work when you have an internet connection. AdviserGo has touch screen functionality, and so is ideal for tablets. It also works on mobile phones (though it would be very small!).
Differences in functionality:
In terms of usability, the two versions are interchangeable, so any clients you create in Adviser can also be viewed in Go, and vice versa. Sometimes you might set up a client in AdviserGo, but then go into Adviser to do more detailed planning, e.g., step-up or down expenses, withdrawals or income, or do more complex planning, e.g., estate planning.
Adviser allows you to set, and amend the 'Liquidation Order' within a plan, e.g., to draw from pension funds, before general investments, or ISAs, etc.
Certain account types cannot currently be entered via AdviserGo, such as trust accounts, EIS, or VCT accounts - these need to be entered via Adviser, and can then be seen in AdviserGo.
AdviserGo has a more limited range of chart views. It does not include 'assets by tax type', 'liquid assets', 'liquid non-pension assets', or 'plan worth'. It does, however, give you the ability to switch from a bar chart to an interactive pie chart.
AdviserGo has a more limited set of reports than Voyant Adviser. The report options in AdviserGo, however, include financial overviews, and also provide the option to generate a single report incorporating inputs from multiple plans/scenarios, simultaneously.
Certain simulations, i.e., the Monte Carlo and Long Term Care simulation, are not available in AdviserGo. In Go, simulations are referred to as "Insights."
Adviser has a step-up/step-down feature which can be applied to income, contributions (to savings, pensions, and other investments), account withdrawal limits, growth rates, inflation rates, etc. This is not available in AdviserGo.
AdviserGo has the added functionality of guided "What if" plan creation, taking you through the most common what if scenarios, as well as giving you the ability to create your own scenarios.
AdviserGo has the added functionality of letting you see whether a client is able to meet certain financial 'goals' by entering an expense as a 'goal', i.e. an objective, and flagging whether, or not the clients are able to meet that objective.
AdviserGo incorporates an additional simulation - the 'Retirement Spending' simulation, which calculates, based on what already exists within the plan, how much the client can actually afford to spend in retirement (as opposed to what they tell you they would like to spend)
In summary, Voyant Adviser is ideal for more complex plans, e.g. to demonstrate tax-efficient retirement planning, or estate planning, since you have the ability to finesse the way in which withdrawals are taken from different assets. AdviserGo is ideal for building simpler plans, but as the two are interchangeable, you can easily move from one to the other.