We started out with an Oasis and did some great trips on it, however if you want to cover long distances on open water or offshore then the AI/TI is definitely the way to go. They can handle, pretty much, any conditions.
When we first got our Oasis we took it up to the Great Barrier Reef and threw it on the back of the ferry for a trip to Lady Musgrave Island. viewtopic.php?f=11&t=8333
It was great for exploring the lagoon but with a TI you could explore the surrounding islands as well!
We have just returned from a 4 day camping trip in our TI. We were able to explore places only a kayak could get to and because we could sail as well were able to go further and with less effort than in a kayak. Our return trip was done in 25-30 knot following winds on open water and we just sat back and enjoyed the 27 km ride!
The simplicity of the Oasis is hard to beat. With the TI comes much greater weight and complexity but these negatives are far outweighed by the benefits and versatility of a sailing trimaran that can easily be converted back to a kayak when needed.