Please recommend me a flash.

Does Canon 430EX justify it's price difference from the sigma one?
Also, 550EX or 430EX? I can get a used one for around $230

Does a 1DMkIIN justify its price difference from a 400D?

In general terms, paying a higher price for a flash/camera/lens/trip​od/whatever can be justified if you can use the additional power/features/capabil​ities to produce better images, or to produce more good images. Individual budgets always come into play.

When it comes to flash units, it depends on how you use it. Different units fit the needs and budgets of different people.

The way to make the best decision is to study the features and specs of different units carefully, read about and understand those features and specs (The EOS Flash Bible is a good place to start), then decide what capabilities you are likely to use often enough to justify their cost, within your budget.

When comparing the Sigma ST model to the Sigma Super, 430EX or 580EX, there are some significant differences. Some people couldn't live without those extra features, and some people would never use them.

Curtis, like ive said in the previous post, I will only use my flash for the family trip, I dont like taking pics using the flash.
I guess Ive just answered my own question then.

Buying a Canon product guarantees that it will work as advertised with the Canon camera and any new Canon camera you might migrate to.

I'm not saying that third party flash units don't work, but the third party manufacturers don't have the inside knowledge of the Canon communications design. They reverse-engineer products to figure out what's happening today with a product. They have no idea what plans are for next year.