I have had both types of deliveries, and they could not have been more different. Of course there is no way to predict whether you would have an easier or more difficult instrumental delivery, but if the latter, it can be very difficult indeed, both on yourself and baby. I would outright refuse any form of instrumental delivery after my experiences. The c-section delivery was far easier on both me and my baby, and it seemed significantly safer for us both.
After a very long and complicated labour, my first child was delivered with ventouse which failed halfway through, then followed by forceps with episiotomy. I tried to refuse instrumental delivery in favour of a c-section, but they made it clear that would not be happening. It was a very chaotic and frightening experience. The baby was almost 9 lbs and in a very strange position, which perhaps made it a more difficult instrumental delivery than others. I had tremendous pain for about 8 weeks afterwards despite being told repeatedly that my stitches were healing well. Walking and sitting were both very difficult during that time. I was still having moderate pelvic pain 6 months later and mild pain several years later. I had rectal prolapse which was resolved eventually but still have a lasting rectocele. I did do pelvic floor PT eventually which finally helped resolve some of the lingering pain.
The other factor to consider is which delivery might be less risky for baby. As bad as the delivery and recovery was for me, the hardest part was actually the effects on my baby. He had severe lacerations on his face from the forceps, including one over his eye which caused it to swell shut. They weren't sure for some time whether it had affected that eye. Also he had a huge wound on the top of his head from the ventouse cup along with swelling. They had to monitor the swelling as whilst some swelling is normal, his was quite extreme and worsening. He quickly developed bad jaundice which was almost certainly exacerbated by the wounds he sustained. He needed 5 days of double phototherapy, and it had gotten so bad at one point that they were discussing performing a complete blood transfusion with us. Luckily, he had a sudden improvement on the 5th day, and it was not necessary. He was a very unhappy newborn and seemed to me to be in a lot of pain himself, as more often than not he was completely inconsolable with a very shrill cry. He was extremely sensitive to anything touching his head for months.
We were in the hospital for 6 days after delivery, and I was an emotional wreck, both because of how awful delivery was and for being terrified for my baby's sake during that time. We could not hold him to comfort him properly, as he had to stay in the incubator under light therapy.
My second child was an elective c-section, after I demanded one. I actually can't imagine a more lovely experience. The delivery was calm and peaceful. I was able to walk and sit better almost immediately after the spinal block wore off. I was getting around far better at 1 week post c-section than at 6 weeks post-instrumental delivery. My total pain throughout this delivery and recovery was probably well under 1% that I experienced with my first delivery and recovery. Baby cried for normal newborn reasons and not constantly inconsolably as my first had. It was lovely to be able to just enjoy those first days and to bond with baby after delivery.
Requesting an elective c-section for my second was one of the best decisions I have ever made.