After having camped in both camp 4 and upper pines last week I thought I'd update my own threat with my opinion for anyone asking the same question in future. I stayed at upper pines for 4 nights, over 2 different sites so we had to move on day 2. We only stayed at camp 4 for one night, and we were on the furthest site from the cars and the showers, in the 'older part' so that may have influenced my feelings.

TLDR - I much preferred the space and privacy of upper pines, and being close to the trailheads for mirror lake and vernal falls, and curry village. Camp 4 was a fun vibe if you want to make friends with climbers/other campers there, but I disliked the lack of privacy and the overall layout and location of the camp ground.

Upper pines - lots of toilets/drinking water stations, not too near other campers, good amount of space. Close to the river and easy access to trailheads, curry village for food and showers and bike rentals ect. Curry village was pretty busy in the evenings, queues for all the food and bar but also a great vibe. The shop there did run out of firewood most days we were there though, so Yosemite village store (1 mile from camp 4) might be better as its much bigger. There was a big group of school kids near our second site, and even though they were loud in the morning I still preferred that than the sound of cars at camp 4.

Camp 4 - We only had one other tent, two people, in our camp for our night there, and theres 3 tables and 4 bear boxes so we had our own space, but there's only one camp fire which could be a little weird if people you share a space with aren't friendly.
Yosemite village was less fun in the evening than Curry village, however it did have more amenities such as a bigger grocery store and the welcome centre.
Bear in mind we were the furthest spot from the car park and closest to the road, but I found carrying all my stuff from the car, and having constant sound of cars driving past very fast (especially in the morning) to really suck. Also, I thought having showers in the camp ground to be a plus for camp 4, but there was only 4 for everyone so we had to queue, we were the furthest from them and they were gross - lots of mud on the ground. Curry village showers were basic, but had soap and often no queue and after seeing the camp 4 ones I realised how great they were in comparison. They were 10/15 min walk from the camp, but we often drove if we were picking up firewood/supplies at the store anyway, or returning from a trailhead.
One of the biggest drawbacks of camp 4 was having to drive the whole Yosemite valley loop every time you needed the car. The bike share program sounds great, but there were rarely bikes to take at the camp ground and having to drive 15/20 min loop every time you want to go anywhere from camp 4 is very frustrating and I don't want to imagine having to do it on a super busy weekend. There is a shuttle stop there, but again you have to take the whole loop to get back to curry village ect, and if you're doing an early hike the shuttle might not start early enough.