1st pressed vinyl best ones to get ?

Generally, a first pressing assures you of getting the earliest stampers made from the 'Mother' master stamper. Logic would indicate that this will be the best stamping. However, 1st pressings do not assure you that you are getting the 1st stampers as each stamper only can output a finite number of records before it is worn out so  1st pressings can also contain 2nd and 3rd stampers etc. depending on how many initial copies were to be pressed for sale. Therefore to get the closest to the Master you should look for the 1st STAMPER which may or may not be included in the matrix info on the 'dead-wax'. To go a bit further, not all pressings from the 1st ( or any ) stamper means that you are getting the best possible sound. Various factors influence the sound quality such as the quality of the vinyl used for each 'batch', the temperature of the stamper during that particular pressing, how clean the stamper was at the time of the individual LP's pressing (those pressed right after a cleaning will sound better than those pressed at the end of the cycle before the next cleaning), etc. There are many variables involved and I have heard many examples of much later pressings sounding better than early pressings based on where in the life-cycle of the stamper that particular LP was made. This is why 'Hot Stampers' demand such a premium - each LP must be LISTENED to and compared to others in order to evaluate which LP sounds best - and the 'stamper' numbers become relatively meaningless. For example, I have listened/compared probably over 50 copies of 'Casino Royale' and most are very good sounding. But the excellent ones are all over the place as far which stamper was used. And even among the best ones there are many sonic differences between Bass, imaging, naturalness of vocals and instruments etc. In closing, if you seek the best sounding LP's you can take 1 of 2 paths. Buy multiple copies of each LP, clean them, listen to each and note the qualities/shortcomings of each LP and do a process of elimination to get to the best one. Or pay the price for the Hot Stamper which is nothing more than having someone else do all the work and incur all the cost of buying the LP's and putting in the time to do the culling for you. There is no magic 'Matrix' numbers that will assure you of a great sounding copy. And unless you are very lucky, you will only find that elusive LP by doing the work yourself or paying someone the high price of having already done this for you.

xlh1- I don’t disagree with your observations about matrix information, but sometimes, there are multiple cuts made simultaneously, to supply several different pressing plants when a record is a high volume one. I know there is information about various Columbia plants pressing for Warners/Reprise and the "1" did not necessarily signify a first, although if memory serves, I think it was associated with the Santa Maria plant, which had very good output. (The "2’s" and "3’s" were cut at the same time, but went to different plants).
The Tom Port thing always stirs up controversy- I’m not going to wade into that other than to say that for a common record, I’ll often have multiple copies of the same record as well as different masterings. It does take time, though. And the pressing to pressing variations of identical records-- my suspicion is, most people are going to look for anecdotal comments (which to be meaningful, contain comparisons) to find a general consensus on "best pressing" and go with that. You must have been borderline nuts after listening to Casino Royale 50 times. I do dig Dusty, though.
PS: also agree that sometimes, a later mastering sounds better, see a couple examples I mentioned above, none of which were "audiophile" re-do's, just later, garden variety commercial pressings. 

Well my 1st pressing of Led Zepp II has arrived and am very pleased with the quality. I don't have a recent Copy  of the same album to compare it to, but can say there is definatly a real rich sound quality to it. I can however compare it sonically to a new copy of Physical graffiti . By comparison the remastered copy sound a tad more hollow . 
Anyway just thought I would share my opinion on the matter .