As a guide I often get asked about which flashback is easiest, cheapest or free to play.

Secondly most often I get asked "what should I go for in a flashback?" 

​

The absolute best choices are the events that offer cars and pets, but are easily achievable in the allotted time set,

which varies from event to event.

Cars gives boosters and pets can be trained

to increase the Loyalty skill. 

If you only want to expand your wardrobe,

look for the themed items you are missing. 

Do you need a mermaid tail?

Do you need fairy wings?

Do you need elf ears?

Do you need Some new profile backgrounds?

Ask your self these questions while looking through your wardrobe and find a flashback to fill this need. 

My website is a cross-reference guide made for exactly this.