I run a blog dedicated to the topics of sex & love in Second Life, and I review a lot of animations and products:
http://hummmagazine.wordpress.com/
Click on the Product Review section to read some opinions.
You didn't say whether you were looking for fixed animations, such as animations in a bed or rug, etc., or in a portable, take along HUD. I'm going to assume the former.
I agree, the TenderLove system is very good as well as portable, and allows both partners to control the action. But it can be tricky to use and set up, especially for a beginner. Akaesha's Kama Sutra system is also good, but again, can be balky and the book-like HUD takes up a significant chunk of screen space. You should try any system before you buy, because the good ones aren't cheap. But then, few of the cheap ones are worth the savings.
In my opinion, TNT is dated, and they don't make any portable products that I know of. Virtual Art Works (VAW) makes a very good portable HUD called the Animtron that uses multi-speed animations, but the sex portrayed is pretty BDSM-ish. Shoki Animations also makes some very good and completely portable HUDS, and they might be your best all-around bet for vanilla take-along sex.. One of my personal favorites is the relatively unknown Sweet Animations. They sell an rug called the Love Box that you can take with you and rez wherever it's allowed, and all their animations are very expressive and hot.
The height of both avatars can be quickly adjusted on newer systems by using the Z-adjust in the Options menu of the HUD, but I'm not familiar with any system that lets you adjust just one avatar except by doing a quick edit using the Position Adjust feature. TenderLove lets you adjust the woman's position by using the arrow keys, but I've always found that feature to be fussy and slow, though it's better now than it was.
I know that you're a beginner, but you should try to familiarize yourself with the basics of object editing ASAP. Most everything in SL requires some object editing to look right, and the faster yu learn how, the better yoiur SL experience will be. Good luck!