I`ve some experience on all of these and I have compiled a list to show the top scorers in each of your requirements. ( in my opinion )
Number one being the best.
fires well with caps :1) MGC M16 ABS (everyone knows the reliability of this design)
2) MGC M16 Metal ( after its been modified )
3) Marushin M16 ( poor bolt design and poor cartridge design let this down, they can work ok for a while but wear quickly )
easy to clean after firing (chamber and firing pin are accessible without too much complications1) MGC M16 Metal ( but only the early type with removable barrel )
2 ) Marushin M16 ( not complex but dull )
3 ) easy to clean however this involves unscrewing the large collared ring at the front and metal onto plastic thread will wear the plastic eventually
accurately replicates original controls (external),1) Marushin M16 ( not a lot different from ABS M16 in detail but its metal man
2) MGC M16 ABS
3) MGC M16 Metal ( really nice finish but external detail not spot on and internals wronger than a wrong thing )
is solid to handle1) MGC M16 Metal (hands down this is far more solid than any other )
2 ) Marushin M16 ( factory built kits are better than build yourself jobs )
3 ) MGC M16 ABS (its plastic and on the M16 there is indeed a long length for it to wobble.)
another category you may need to know
spare parts availability should the unthinkable happen ( or inevitability ) 1) Marushin M16 ( still in production Francky or Shaz will be brilliant )
2 ) MGC M16 ABS ( still a few floating about but spares may be hard )
3 ) MGC M16 Metal production stopped a long time ago and certain parts ( bolt heads ) will be nigh impossible to find
I`ve mentioned the Metal M16 with removable barrel , this is because they are much more easily cleaned and are front venting , the later Metal M16s have a blocked chamber, fixed barrel and drop one point and are harder to clean.
If I was only allowed to buy one and based on some years of experience I would go for the early version of the Metal M16 , its solid , looks great, easy to clean and works well ( once its been modified to use modern cartidges )
Worth noting that UK spec early metal MGC M16s have a blocked (but removable) barrel but Japanese versions are removable and open.
hope this helps
DOC
Edit : for gods sake dont say they all look the same Madmike will blow a gasket
Edit again ..I dont have a preference between M16 and XM models really although worth remembering the MGC CAR 15 has a fixed metal stock ( whereas the other two versions are ABS and move )