VM-68: Used it back in the 90's when I was a young skull full of mush teenager. I used it as a rental, and it was a good solid, reliable chunk of metal.
Tippmann custom 98: Tough, dependable marker. I used it at several fields as a rental. I was going to buy it instead before I stumbled upon the BT line
I have also used several Kingman markers, mainly the Spyder line some years ago. I never had a very favourable impression. They tended to jam a lot as I recall. I don't know much about their newer designs.
My current marker is based on the BT-4 Assault model. Current upgrades: BT-4 Magazine expansion chamber (works well, and makes it look more like an M-4 carbine), remote coil (a 20oz CO2 tank is not light. This helps), Ops Gear carry handle picatinny scope mount (Let's me mount optics high enough to use with a mask.), NcSTAR red-dot sight, Ops Gear M16 / AR15 hand guard picatinny rails (allows me to mount the forward grip under the barrel, where it belongs), JT-Tactical 3 point sling, an aluminum valve/power-tube combo, and an Empire motorized hopper.
Remote coil: It's heavy. Removing the CO2 tank helps big-time.
Sling: See above.
Magazine kit/Magazine expansion chamber: Makes it look more like an M-4 Carbine. Look the part.
Aluminum Valve/powertube combo: Under sustained fire, the CO2 can get cold enough to crack the plastic of the power-tube. Aluminum is made of sterner stuff.
Tough, cheap, easy to upgrade.
It ain't light, and the feed-neck is non-standard, and difficult to offset.
About a year ago I decided to seriously get into paintball. I had been going on and off since the late 90's as a renter, and decided to become an owner. I was looking for something that looked the part, as the neon coloured speedball type markers looked too much like a toy to me. I also did not want to spend too much, and I had the C98 as my initial target.
It was around that time that I stumbled on to the BT line. I was automatically drawn to the assault model, due to it's looks, and favourable price. It was a good match.
The marker is a solid hunk of metal and plastic, with the bulk of it being made of machined aluminum. The few plastic parts are also pretty tough, especially the collapsible stock. Also, the picatinny rails, and AR-15 carrying handle allow you add real-life rifle accessories to it.
My field experience with it has been exceptional. The psychological impact alone of such a fierce looking marker is worth it. Just try showing up dressed in BDU's, toting this marker, and you've already terrified most casual players. The reliability of this marker is high. I've logged 9+ hour games, with many marker hits, and jumps to cover leaving it covered in paint and grime, both inside, and outside, and it functioned without a hitch. The only problem I had was the plastic power-tube cracking after firing a good 200+ paintballs without pause using CO2. But, that rarely happens in most games, and it was after a good year of use, week to week.
On another note, I can count the number of ball breaks I've had on one hand. I've put this thing side-by side with A-5's and X-7's, and I can assure you my paint was breaking on my target, not in my marker.
This marker is about as solid as they come. It comes out of the box accurate, and deadly looking. Ball breaks have been almost non-existent. The marker does weigh a good deal, but the weight is well balanced, and reassuring. It can accept a blinding number of upgrades (Ops Gear is your scenario friend). Last, but certainly not least, it won't break the bank.
The bottom line: Tough, cheap, upgradable. A good buy for any budding scenario/woodsball player.