I upgraded from an Iphone 3GS to an Iphone 5 in December. I'm happy with my decision, but honestly think it really depends on your needs and how you use your phone. You can see the side by side comparison of all three current iPhone models on the Apple website: http://www.apple.com/iphone/compare-iphones/ .
My opinion is that there isn't a whole lot of reason to upgrade from a 4S to an iPhone 5. For me, I needed the 32GB phone which tipped the scales for me, otherwise I probably would have gone with the 4S. Having the fastest processor is nice for the future and keeping this one more 'current' speedwise, but my husband has a 4 and I don't see any difference in speed in terms of apps opening and game playing, currently.
The other big upgrade with the iPhone 5 is of course, the 4G LTE connection. I do live in an area with that availability and it's pretty darn sweet. But 3G will get the job done, albeit more slowly, so again it's all a matter of how important that lightning quick cellular data connection is to you.
As far as the connector, it's a slight inconvenience to have to charge my phone with the one cord that came with it, when my household is littered with the last generation connectors for phones/ipods/ipads. But in defense of the new connector, it is really fast - I used to have to leave my phone overnight to do a full restore due to the amount of music, photos, videos and apps I have on it. This new adaptor was noticeably quicker for syncing and moving data to the phone.
Hope this helps! I think both are great products, it's all about whether those minor tweaks with the 5 are worth the extra $100+ to you. Regardless, it's nice to have moved up from my 3GS which was starting to feel S-L-O-W with some of the multi-app demands I was putting on it. Good luck!