Right now, the 144 has the best price/performance... if you can find one cheap enough. If you can only get one for $10-20 less than a 146 or 148, as retailers seem to be charging these days, the extra multiplier may be worth the money. However, a 144 will reliably get you around 80-90% the overclock of a 146/148 with many 144s hitting the same speeds, so if money is of an issue, a 144 is the way to go.
Similarly, a 165 generally will not overclock drastically worse than the average 170/175 so it is ultimately a better buy if money is more of an issue than maximum overclock.
But with prices the way they are these days, While 144s and 165s are generally cheaper than 148s and 175s, the former are drastically marked up while the latter are much closer to AMD's MSRP, which only complicates things further...