I am considering spending a few days in Khao Yai national park.

Does anyone have any experiences they can share ?

I have been there numerous times. If you are going to stay there 'a few days', you might be better staying at one of the resorts just outside the park in Pak Chong.

They offer more in terms of activities.

If you wish to stay in the park, you have a choice of 2 campsites (i.e. tenting) or somewhat overpriced (well, it is a pristine forest) National Park bungalows. The campsites will be full at the weekend.

Activities inside the park include swimming in the waterfall, eating, drinking non-alcoholic drinks, bird-watching, spotting animals at night using lights and hiking.

If you are feeling more adventurous and have cash to spend, why not hire a ranger and hike the short trip to Khao Laem. Zero tourists and a chance to spot tigers. This is again within the National Park but you need a ranger to take you there.