I have previously owned the LiquidMetal, Flexpoint and Microgel versions of the Instinct. Out of these three previous generations, I felt the LM was the most powerful and offered the greatest control. Many other players have felt the same way...
Apparently Yen-Hsun Lu, who beat Roddick at this year's Wimbledon to advance to the Quarterfinals in 2010, is rumored to use the LM Instinct with a paintjob! Other notable tennis pros that have used the Instinct (in one form or another) before include: Agassi, Kunetsova, Myskina, Gasquet, Karlovich, Azarenka
This YouTek model feels to be a bit more solid and able to generate faster swing speeds on contact. It is about the same weight and balance (slightly head-light) as the others, and also shares the dense 18x19 string pattern which I prefer for better ball-pocketing. Also possibly because of the d3O construction material, I felt like this one was more maneuverable at the net and my volleys felt crisper than my other Instincts.
With the YouTek version, I felt that I could definitely swing faster than normal while keeping up the momentum and not spraying the ball. The only downside I felt initially was that it is stiffer than the other models, and I felt more shock in my arm but eventually got used to it. Serves and returns were about the same, but I felt more confidence in swinging all the way through the contact and into a full follow-through with risk of the frame twisting much.
I also like the fact that on the inside of the grommets are painted the markings for where to tie the knots and weave the crosses. This comes in handy if you ever need to string a racket (later I will post an article on how to string your own racket and where/how to buy your own strings to save time/money in the long run).
Better at the net than previous Instinct models
+Solid swing weight and frame composition (d3O tech)
+Head kept most of the positives from the previous LiquidMetal Instinct version
Grommets are functionally painted to help stringers
Stiffer frame (good/bad depending on your preference)
Styling has a bit to be desired - it looks a bit plain to some people
Cost: $139-$159 (retailed price currently)
Tennis-Bargain.com Rating: 4.2 out of 5
So there you have it, I would recommend the YouTek Instinct for baseline or all-court players with a 3.5-5.0 game. You should have a med-long swing pattern as well.
For those looking for less power, I would recommend the Microgel Instinct or the Radical line, which is also slightly heavier. For someone with a more compact swing or generally wants more power I would try the Head Liquidmetal 4 which is still on sale for a very good price.
Please email me at TennisBargains@gmail.com for other questions or help picking a racket right for you.
For other racket reviews, check out the Tennis-Bargains.com Reviews page