Airsoft Forums UK

My first choices would be:
TM Hi-Capa - hicapahub.co.uk is a hell of a drug. Can build a hicapa to do basically anything and they shoot well out of the box
AAP-01 - Has a fun switch and highly customisable, but needs a few upgrades to get it good (and not eventually blow itself up)
KWA mac11 - Haha gun go brrrrrrrrrrttttttttttttt. Can get a SMG thigh holster that fits it well, or a shoulder rig.

I've always been an advocate for GBB sidearms anyway, as most of the time when I need my pistol I need the extra firepower that the squishy double action trigger of the mk23 just doesn't give; if I want to go undetected and they're within my MED, I tend to just go to ground and let them pass. When it comes to GBB sidearms, it's basically just "what TM pistol do you like best?"

If you want to keep with the NBB, the TM Bodyguard 380 or LCP2 are solid options. Get the Hadron TDC upper for it and it'll shoot with decent accuracy within your MED, plus it's nice and small. Alternatively, for mk23 mags I've had a lot more success using the clone mags with TM feed lips and Nineball routers (the clone feed lips and routers are ass). They don't leak as much and any leaks that have happened I've managed to fix fairly easily.

I have been using the asg mk23 with all the upgrades.

Magazine wise it's been the asg mk23 magazines with  laylax 9ball fill valves. 

Maybe I'm just unlucky or have some really duff mags. As I love the pistol but hate the mags with passion

A common trend. A lot of people love the pistol, but hate the mags, trigger or both. Sounds like you've been unlucky, as I've had no real issues with my clone mags and I don't think anybody I know who uses clone mags has had too many issues.  

i would guess you do the usual with your clone mags @impulse . That being putting the silicone sealent around the base of the main magazine body to stop the leaks from the base. occasionally regrease the o-rings on the fill valves.

I usually use ulra-air as a gas for my mk23 so wonder if thats the issue

I haven't done the silicone sealant around the base. I try to take them apart as little as possible because it's a faff getting the baseplate back on. I use the regular nuprol 2.0 gas in mine, so a bit more lubricant in than the ultra-air, though I do like ultra-air as well. I just never leave ultra-air in my mags as I've heard it's dryer. One of my mags was leaking when I bought it, but the o-ring was crap so I replaced it with an o-ring from one of my (many) leaky TM mags and it worked like a charm. Haven't had any issues since.

cheers @Impulse I may have to try and order new fill valves and try a different gas in them just incase then.