Electrolysis is not like laser - it will handily take care of any size hair, any color of hair on any color of skin. The skill level of your practitioner is the most important thing to consider. Sample as many as you can before you decide.
If she/he has proper, quality magnification then they can actually make better more accurate insertions and it doesn’t hurt as much. Also, she/he can see any slight skin reaction on the surface of the skin and quickley adjust the heat setting and/or timing.
Next, any method used is effective. Any method can leave marks or any method will not leave marks. Practitioner skill and how she/he uses the equipment is the key. Thermolysis is more cost effective because more hairs per minute can be removed. I am a fan of microflash thermolysis. With up-to-date computerized equipment one can do wonders as far as sensation and skin reaction as long as the skill factor is present. These are powerful epilators, but have a full range of adjustment options that can easily handle man hair or soft very small teen upper lip hair on very moist skin. The modern electrologists epilators have awesome range and capabilities. These machines can do all methods of electrolysis, galvanic, blend and thermolysis.
I like blend a lot, too. It takes longer per hair, but is extremely effective. I will demonstrate both methods for my clients and let them feel what they like best and what is best for their skin type and reaction. Most choose microflash thermolysis, unless I tell them that I must do blend for such and such reasons.
So if you can find someone that can easily and skillfully use both methods, that would be just peachy. If not, choose the practitioner who is skilled at one or the other and you will be just fine. Watch your skin reaction while healing, and you should not feel like you are being plucked. In the beginning stages of hair removal, you may feel some hair resisting, but that can happen with the intial clearing.
If your skin reaction is such that you feel like you have to hide in the house for a week or two, TALK TO YOUR ELECTROLOGIST so she/he can use another strategy for your skin. Keep a close relationship with her. Okay?