another vote for MNR because of there build Q. I own an mk indy and i wouldnt touch a westy or a caterham, because i cant justify the price tag of either over Mk Mac1 or MNR.
BUT it does really go on what u want one for and budget. I would own a westy/caterham if i was older, less into 'racing', had loads of money and wanted triditional styling and the 'name'. But thats IMHO.
If u want to build yourself then i still recomend the cheaper kits as u cant cut corners on the 2 big guns and any one off modes look odd due to the styling.
go to a few shows and look about at them all, talk to the owners to get some idea of what they are like to own. Its the only way ** going to know, as mags/internet doesnt come close.