I weight about 135ish and I'm a 29/30 size pants
Medium, i'm the exact same weight and waist as you. I have worn both abena air plus and x-plus medium, both fit me fine.
And in general you want to be on the lower end of a larger than than higher end of a smaller.. you'll get a better fit. Tranquility pullups smalls go to 32 inch waist and i havea 30 but they sure don't fit well. The mediums go from 34 to 44 and they fit me great. This was when i first started to buy "Real" diapers a month or so ago.
Im a 31" waist (but was 29/30 until recently ) and although ive always used mediums fancied trying the smalls as they do look quite nice, luckily I just got 2 as they didnt fit at all and were very uncomfortable!
definiltey get medium.
Personally, I'd suggest going with the small. I am 5'10 and about 155 with a 32 waist, and I still wear the small. Granted, I love a tight fitting diaper. It isn't over the top tight, but it's at the limit of that size range. It just sucks, because I've tried the mediums and it just feels so huge on me. Too much wiggle room. This is just my opinion, but if you like a tight diaper, go with small. If not, hit up those mediums!
I have tried M4's, M2-Air plus, and S4's. I'm about 32" waist at 130 lbs and 5' 11" but the Smalls fit just right on me. The waist band is low so its really easy to cover up with underwear and it can last me up to 5 hours through the day with normal wetting. The only I can see that this might have is if you were to get a raging hard on and wanted it to stick up, it would probably stick out of the diaper. Anyway, being that I'm a 32" waist size, the tapes just barely touch the front wing so it is quite a tight fit, but the fact that the absorbency is adequate and its rather discreet is enough to make me not regret getting a bag of them.
I would still recommend Medium though. There's definitely a lot more room to play around in them and they aren't so discreet due to their thickness, but man are they ever comfortable and sexy.