I am wondering about hair transplant, which is best FUE, FUT, multi unit hair grafting?

FUE is only a harvesting method.  Patients choose the FUE method to avoid the linear scar while accepting it may not be optimal in growth.
You must understand most people would not notice the linear scar unless you buzz your hair very short.  
If you are considering surgery it is best to see a doctor to understand your options and have a MASTER PLAN on how to address your hair loss

My opinion for a patient such as yourself who is looking to simply increase density to a slightly thinning hairline is that an FUE or FUT follicular unit grafting procedure would be the best for you since it will provide improved density with individual hair follicles.  This will provide a much more natural hairline result.  Good luck!

Both FUE and FUT (Strip) can provide excellent result when in the hands of a skilled surgeon and team who have mastered their craft, and both techniques can provide poor results if you do not choose a top clinic.

A great first step would be an online consultation. Often you can submit photos to top hair restoration surgeons for a complimentary evaluation. This should help lead you in the right direction. Having multiple consultations with different doctors cannot hurt. 

Hair transplant via FUE (follicular unit extraction) or FUT (follicular unit transplantation) can be successfully performed by either harvesting method. The major difference is that FUT will leave you with a posterior scar.  However, if you never plan to wear your hair really short, no one will see the scar. FUE typically costs a little more than FUT.

The many techniques use in hair transplantation, when performed in skilled hands, works well and comparison is not needed. What you need to to have a good doctor work this out with you

fue and fut refer to harvesting technique used to get hair from donor zone in the back of the head.  If done by a specialist they should harvest enough and good hair with both techniques.  However there is more involved with the hair t ransplsnt procedure then just harvesting of the grafts. For fue we need to shave the donor zone to harvest, so for female clients who do not wanted to shave their hair fut is a better choice. 

Hairs grow in groupings called follicular units. These units in Caucasians will have on average 2.3 hairs per follicular unit. The results of surgery will depend mostly on the skill of the surgeon and their team. In general, density will be greater with FUT rather than FUE as survival of grafts is better and deselecting of larger units(3-4 hair units) is not done with FUT as with FUE. Most importantly, find a well qualified full-time hair restoration surgeon to guide you to the best method. Also, need to make sure you are a candidate for hair restoration and avoid a bad hair transplant result.