Its been argued quite a bit, every difrent way. I personaly think that while BV1 was quite notorious for having a few very excelent values, BV2 tends to be quite good. Armor is still probably valued too low, so mechs with more armor and less guns tend to be the better values, while over armed mechs tend not to be, but its a lot less than it once was.
In general, the key to being a good player and a good bidder is getting your money's worth. Jump jets are pricy, so people often point to ground bound mechs as good values, since they offer more guns for less BV. But, if you've been clever enough to select terrain that will favor jumping mechs, by being broken, or by forcing close quarters combat, or by having plenty of water features, or by what ever other reason, then the side that takes 'poor value' jumpers will tend to win. If you take C3, which is very pricy, especaly at larger levels, then you'd better have mechs and tactics and a map that will let you put your C3 net into action (and hope you're opponent is not a hot hand with his ECM mechs). Better pilots, mentioned below, do drive cost up, and quickly. Even for me, as a proponent of better pilots, by the time you get to 0/0 its pretty qustionable. But, if you've got fast mechs and an open map and you can keep the TNs generaly very high, then you can really get some excelent value out of better pilots, and a force that takes the field with half the amount of power and armor can win by hitting four or five times as often, and turn what seems like a one sided route into quite the upset.
Its the skills to use what you've paid for, rather than getting good value, I think that is more key.