Is it more affordable to buy the Annual Travel insurance policy or Single travel policy if I travel multiple times a year?

User friendly.

Annual for sure

Generally, annual cover is better for multiple trips.

Sometimes, we may go JB with friends and forget to buy travel insurance also.

Additionally, single trips usually doesnt cover preexisting conditions, so if you treat travel insurance like a normal life/medical plan, better. ie pay for travel insurance through your whole life.

There was a big scare last year where a citizen's
medical repatriation flight for major stroke overseas was delayed because the air ambulance service wanted to check if the guy had preexisting conditions before flying, but it was the weekends, and medical records offices were closed, so they were delayed a few days.

Though lately I saw some amendments to some repatriation clauses to include preexisting, better be safe than sorry.

Few things to consider are the frequency of your trips, the regions you're going to, and length of your trips.

In a thumb rule, if you often go JB for a short getaway, or flying a lot. Then thy getting Annual Plan when they are on sales or through rebate program like ShopBack.

unless you always purchase your flight tickets with your miles card that gives you free travel insurance, then you might be able to take a step back and only buy single plan for bigger trips that you need more coverage