Very difficult question to answer specifically but quite easy to narrow down your choices.
Clearly you need an Annual Multi Trip policy if you travel frequently. If you do not travel to worldwide destinations then buy a Europe only AMT policy. If you are likely to spend a significant amount of time away from the UK then check that the maximum trip duration is suitable (normally this will be around 31 days but easy to get it longer). Also check that there is not a maximum length of time that you can be out of the UK in total during the year i.e. 6 months in total.
Most will come with winter sports included but often this is only 17 days per year so if you plan to do more than that then you need to find a policy with a longer limit.
As for benefits of the policy this is really down to personal choice but the main ones to look for are Cancellation, make sure the benefit is likely to cover the total cost of each individual trip you will take. Baggage, if you do not have home contents cover then this will have to be sufficient for the value of the personal effects that you take with you. Also make note of the inner limits that relate to single articles and a combined limit for valuables.
The medical cover on all policies are likely to be sufficient no matter where you travel in the world. Although if you are planning to travel to America then you should avoid policies that have a benefit of less than £1,000,000.
Hope this helps.