Best set for a new set builder

[Griffins]

I'd vote for a smallish set, to make it easier and not get bogged down. Pick and era you like, or players you identify with, and start plugging away. The nice thing about a small set as opposed to a larger one is that you can complete it and jump to the next era, giving yourself a wide range of represented players over time
Pre WW1
T201- 50 cards, Cobb and Matty, overlooked and somewhat undervalued
E95 and E95- small sets, lots of color, good player selection

20's
'21 or '22 Exhibits- reasonable cost, fairly attainable, all the stars of the day- Ruth, Cobb, Johnson, etc

'30's
'34 Goudey -96 cards, good player selection, but not Ruth. The high numbers are not as tough as they are supposed to be, IMO
'34-'36 Diamond Stars - 106 cards, or 96 if you stay away from the high numbers, which are repeats of the lower 96 and tough to find. No Ruth or Gehrig, but a strong selection of players, great design, and the thick cardboard stock makes them more presentable when well worn

'40's
'41 Playball. 72 cards, great design, all the stars of the day. Dimaggio, Williams, Greenberg, etc

'50's

'53 Bowman. Best design of the post war era, IMO. 160 cards flawlessly produced with just good, clean photography. Mantle, Feller, Spahn. Downside is no Ted Williams or Jackie Robinson.

'54 Red Heart - 33 cards, good player selection (Mantle, Musial, Snider) but no Robinson or Williams. Very attainable

'56 Topps- 342 cards (354 if you add the team variations), but the first year there were no conflicts between Topps and Bowman so you've got everyone except Musial. A bunch of variations make it interesting.

'60's

'63 Fleer- 67 cards, most major stars, just two tricky shortprints, Adcock and the checklist, but those aren't as tough as you'd think.

'64 Topps Giants 60 cards, every star of the era, easy to find.