Best Events to buy during 100 gem sale

The diggy's adventure team has done something nice during the world crisis of 2020 - All events that were released before 2015 are available for 100 gems. Following is the list of the best events you should buy in my opinion.

Note that since these events are before 2015, they are unsegmented, that is, cost same for all regions. So lower regions may benefit very well from equipments of these while higher region can only expect to do them fast because of low energy requirements and also increasing their gems and basic resources.

1. Christmas 2015

Edit: The discount on this event was discontinued on 6 October, read on from the 2nd one.

This one is the best story every, and best part is it's now available for 100 gems. If you've never done this, go for it!
But before you buy, collect atleast 200k-300k coins. There's some great equipment that sells for just coins (2x2 1100 storage thrice - Min level 77, 2x2 220 regeneration thrice - Min level 74) so that gives a great boost.
If you're in a higher region and don't want equipment, you can use vouchers to buy green rings in Christmas 2014 (2 vouchers for 1 green ring) if you're considering buying that as well.
If you're doing this for the first time, you get 602 gems! Even if not the first, you get 352 gems so if you have the time and want to increase your gems, you can do this again and again while the sale lasts.
Completely clearing costs 4 million energy but you don't need to do the challenges if you're in egypt or even scandinavia.

2. Christmas 2014

If you've got everything from Christmas 2015 or just bored to repeat, this is the next best one
You can get some good equipment especially in the lower regions but the voucher equipments of this story isn't as good as Christmas 2015. You can use the vouchers of this story in Christmas 2015 so if you plan to purchase Christmas 2015 again, consider saving your vouchers from Christmas 2014 and using them in Christmas 2015 instead.
If you're doing this for the first time, you get 178 gems. Second time onwards, you get 78 gems so not really worth repeating..
Completely clearing costs 722k energy but you don't need to do the hard parts of the locations.

3. Christmas 2013

Another christmas story! Well, these have more mines than other events so these are most recommended.
But the equipments aren't great compared to Christmas 2014 or Christmas 2015. But you can use the vouchers obtained here in Christmas 2014 or Christmas 2015. If you're in Egypt, get equipments from Christmas 2015 or if higher, get green rings from Christmas 2014.
Total energy required is just around 300k, since this was one of the early game events and higher regions didn't exist back then.
You get 120 gems for first play and 60 gems for repeat play so recommend playing just once.

4. Easter 2015

If you need a new story after the first 2, this is another one that gives surplus gems compared to sale cost.
You can get one good piece of equipment (3x1 750 storage or 3x1 132 regeneration - Min level 90) if you do the challenge location as well (Total cost is 140k energy, although you don't need to dig all the tiles).
If you're doing this for the first time, you get 122 gems. Second time onwards, you get 47 gems so not worth repeating.

I guess those are all that are good enough for all regions, good equipments for lower regions or a gem surplus and basic resources for higher regions. And ofcourse something to play with if you're bored at home.

Other noteworthy mentions

If you just want something new to play everytime, here are a few more you can consider.

Event	Approx energy required	Gems gained for		Why
Event	Approx energy required	First play	Repeat play	Why
Independance day	1.79m	119	44	2x1 135 regeneration equipment or 3x1 700 storage equipment if you also do the challenge mine.
Diggy's 1st Birthday	113k	111	111	Gem surplus (if you double your quest rewards).
Diggy's 2nd Birthday	310k	115	65	Gem surplus for first time play.
Wild West	340k	104	9	If you are in higher region and don't want equipments, there are green rings in shop for this event, and 4 extra gems than purchase cost.