Should I upgrade my iPhone 3GS to the 5C or 5S?

I live in the UK by the way.
I currently have an iPhone 3GS, which I love, but I'm giving it to my mum because she needs a phone. Plus it's simple for her to use, haha.
Anyway, I really don't know whether to get the 5S or 5C. I was thinking about getting the 5C as it is cheaper, however I'm worried about using it as it is such a big leap from 3GS! I'm not sure? I have compared the specs for both and they both look fine to me. Decisions, decisions!

By the way, I'm not getting one because they are "on-trend", it's because I like Apple phones, they work well for me. Plus I'm not the kind of person to buy mobiles every single year, I've had my 3GS for almost 4 years now.

Thanks.

Added (1). P.s. Please don't leave a comment b*tching about Apple or telling me to go Android, I just need help with my decision.

If you want save 100$ and want to use plastic go for iphone 5c
i think you should go for iphone 5s

Might as well buy the better 5s since you don't upgrade often. I prefer Samsung and am upgrading to a note 3 when it comes out. Look at a site called phonearena than look up a note 3 and iPhone 5s if they have it up yet. The note 3 is far faster but I just like it when people use Samsung.

I'd suggest you get an iphone 5 - there's next to no difference functionally between a 5 and a 5c, but the 5 has a much better casing than the tacky looking 5c models.

The 5s is an option if you really need any of the extra speed or facilities.

Because a lot of people will go for the new models on principle, the original iphone 5 should also come down a bit so be better overall value.

If you are willing to wait about a week then get the 5s but if you really want a phone today get the 5C.