the problem w/it being on your panties is it's there until you remove them & must put up w/the uncomfortable wetness which could be all day! the vagina needs to breathe. while the vagina creates moisture, excess wetness can cause itching, irritation & lead to infections. that's one reason the advice is to wear cotton crotch panties & avoid tight clothes & extended lengths of time in pantyhose or wet workout wear.
at least with pantiliners you can change them throughout the day vs. being stuck in sticky wet underwear. changing to a dry liner is healthier & more comfortable than having to spend the whole day w/funky panties.
I've used pantiliners for 32 years with no problems. I did have some irritation w/one particular brand because of their stay dry covering. It could be that you're sensitive to an ingredient in the brand you use. Firstly, I'd switch to unscented if I'd been using scented/deoderant. If that didn't help, I'd switch brands until I found one I that didn't bother me.
Some ppl have more than a 'moist' vagina & need pantiliners. There are plenty from which to choose, so you've got some experiments to conduct. To consider: do you use the same brand in pantiliners as you do pads? (I don't.) If so, do the pads cause irritation, as well?
*Also, it could be that your irritation isn't related to the products at all and the blame is misplaced. Since you've used them for 7 years w/no probs, the culprit could be a change in detergent, soap, or any number of everyday things. No douches becuz the vagina is self-cleaning. The moist towelettes the toilet paper companies have on the mkt can cause irritation in many ppl. No feminine hygiene sprays-not needed.(If there's an unpleasant smell, then one should be checked for infection instead of masking it w/spray.) You could even be reacting to sperm, condoms, spermicides or the like in the sex-related realm. Many women become irritated or itchy shortly after their periods due to the hormone fluctuations. The list is quite extensive, but the items I've listed will get you to thinking of all the products with which you come in contact.
What does the doctor say the pantiliners have within them to cause irritation? Pads & tampons are government regulated to be safe, hold specific standardized amts of liquid, & other tidbits of trivia. Liners are created from the same materials as pads, so I wonder where the idea that they're bad comes from.
I vote pantiliners.