Botox needles are very small, much smaller than most needles for fillers and the volume is less also, for most areas after a mild topical anaesthetic I couldn't even feel them.
I found it depended on the area around the eye and the type of filler. I believe I had Juvederm but not 100% sure. I have had both Restylane and Juvederm in other areas and under the eyes was the most uncomfortable but I wouldn't say it was painful. If you use a strong topical anaesthetic (they had 25% lidocaine gel at the place I went to, left on for 30 mins) and then ice, it is not more uncomfortable than using the fillers with lidocaine added as an injectable. I have also had a hyaluronic acid + vitamin C filler to top up my under eye fillers and help with new collagen formation and for these I only had a mild anaesthetic. They used smaller needles on the vit C but the solution burned. All in all it was not uncomfortable enough for me to stop getting them, I had about 6 sessions with the vit C and several others with brand fillers.