Manchester flier advertises 300 tables.
W. Springfield postcard advertises 1000 tables w/members of the Winchester Arms Collectors Assn (WACA) and members of the Remington Society of America (RSA). This translates to a number of tables (perhaps 100-150) of pure collectibles that usually start with prices in the $4K+ category. Nice to look at, prohibitive to purchase.
Since there is a conflict, some vendors who tend to work both DiPrete Promotion and Mid Hudson Promotions shows will be at one and not both shows.
Lots of "national" vendors come to the Big E shows and would never travel to the smaller shows.
Handguns: LOTS more for sale in NH, but generally we can't buy them so it doesn't matter.
Hi-Cap Mags: Prices will probably be cheaper in NH than MA. You need to be careful, as what you buy in either place could put you in jeopardy for 5 years and $5K-15K fine/mag. Also you would lose your legal ability to EVER possess guns in the state of MA.
I've seen lots of LEO-Only marked mags for sale in both NH (pre-9/13/04) and MA, just laid out on the tables with no attempt to restrict who they were sold to.
Reality is that Big E will probably have 600ish tables of items for sale (their advertised number of tables is always "optimistic", more likely reflecting the number of tables that fit in the room, not the number of tables sold). A number of book dealers, accessories and supplies, lots of rifles and a smattering of handguns for sale. Most guns are priced high vs. a good local dealer. But the variety of supplies makes it worth a trip.
I'm planning on spending 10/9 at the Big E and Manchester is probably 1/2 the distance.