What type of hunting will you be doing? If you want a great machine and $ is not a factor then the CTX is what you want. It is waterproof (V3i is water resistant NOT water proof) and can be taken to the beach and into the water (no water hunting with the v3i). The CTX with the new salt water update was recently tested by jas415 at Galveston with NO issues. Minelab does issue updates and changes to the function and performance of the CTX. Whites? Well they did offer an update from a V3 to V3i (free if you were a pretty recent purchaser when it was released) otherwise more $ for the upgrade/update. No USB connection for V3i. On the CTX you can modify/create new programs for the CTX on your computer and load them into the CTX or share/trade programs with other users. V3i? Nope. You program the detector through a series of menus on the detector itself.
However... IF you are new to metal detecting the CTX is a very BIG step. It will confound you, frustrate you and then AMAZE you when your brain and your CTX get in sync. In the Houston area, we are fortunate to have a very good Minelab dealer located in Spring Texas. They can answer most of your questions even if you decide on another brand. They can also help you get up to speed with it.