Which is the best speaker to buy ?

I currently have the Audio Research LS25 MK2 preamp & the Audio Research 100.2 amp with the denon 3910 universal for my source and totem forests for speakers which I want to upgrade. What would you recommend out of these choices or mabe another, Von Schweikert, Wilson sophia, B&W nautilus or usher?
wow, unless you are going to the top of the line at the above mentioned brands, the forests compete with the choices listed. what character of the forest is driving you away?
If you're determined to upgrade the speakers, I would recommend auditioning as many as you can. Personally, I'd upgrade your source instead. I think you'll get more reward for the effort, and the rest of your system is already very good. Just my two cents.
Out of you three, I would choose Von Schweikert. Other options Vandersteen Quattro.

What are likes and dislikes of your Forests?

I have never heard the 3910 but, Boa2 maybe be on to something. "I'd upgrade your source instead. I think you'll get more reward for the effort, and the rest of your system is already very good."
Save your money and add a subwoofer (probably from Totem). You get the biggest bang for the buck that way. Your components are fine.
Your amp should drive Wilson Sophia or B&W 803D no problems. B&W Nautilus is the previous model. D series is new and better.

I don't think your amp will drive B&W N802 or 802D the way they supposed to be driven. So B&W 803D would be nice.

How do Totem Forest speakers compete with Wilson Sophia or B&W 803D?
I have a pair of Sophias and they were killer with an ARC VT100 Mark III that I used to have. I would think your amp would work well with the Sophias as they are a relatively easy load other than being a nominal 4 ohm impedance. I don't have experience with the other speakers but they are also highly regarded.
Consider Proac D25.

I heard these driven with your amplifier two days ago at the dealer.

I was very impressed to say the least!
Totem Forests are pretty good as far as two ways go...although I don't like two ways as they get bigger...(Mid range suffers a little when coming from 6" or 7" cones, IMHO. So the best two ways tend to be on the smaller side of things...)

I would consider a proper three way to take you to the next level (more dynamics, mid range clarity and better bass).

Several of the speaker manufacturers you mentioned are safe bets for good quality...just try to audition some three ways (with a dedicated mid range appropriately sized).