At this point, I've stayed in over fifty different hostels in various countries around the world. As I'm still on the road, I'm sure that number will only continue to grow. For now, though, I have a a few favorites that stand out to me as the best hostels - whether I loved their atmosphere, location, awesome staff, or some combo of the above. It was hard to rank them from most to least favorite, so I ultimately decided that chronological order was the easiest way to approach it. 

If you click on the names of any place, they'll take you to each hostel's website. 
Here are my Top 12 favorite hostels so far:

1. Hostel Bekuo - San Jose, Costa Rica

Date of Stay: 6 May 2013
Why I Liked It: Walking distance from the city centro/ Affordable/ Cool staff/ Clean/ Breakfast included/ Pet bunny that was super sweet and bounded around my feet in the lounge.
Potential Unlikable Aspects: Open, tile rooms mean you can easily hear boisterous neighbors. (Pretty standard room style for Central American hostels, though).

2. Lofoten Å - Å, Lofoten, Norway

Dates of Stay: 28-29 August 2014
Why I Liked It: Adorable twin room in a cozy two-bed cottage with a nice kitchen/ Views of the mountains abound/ Well-kept/ Next to a quaint historic area with museum, bakery, & general store/ Close to incredible hikes.
Potential Unlikable Aspects: Small, fills up fast/ Pricey like hostels in all of Scandinavia

3. Långholmen Vandrarhem - Långholmen Island, Stockholm, Sweden

Date of Stay: 7 September 2014
Why I Liked It: Housed in a refurbished prison/ Hotel style on a hostel budget/ In a beautiful part of Stockholm/ Friendly staff/ Twin-bed "cells" come with attached bathroom and shower/ Washer & dryer available for guest use.
Potential Unlikable Aspects: Pretty pricey, like much of the accommodation in Sweden.

4. Landsorts Vandrarhem - Landsort, Sweden

Dates of Stay: 10-11 September 2014
Why I Liked It: Awesome location in a tiny island village at land's end in the Stockholm archipelago/ Underneath a lighthouse surrounded by abandoned WWII bunkers on rocky Baltic coast/ Well-equipped kitchen/ Nice facilities.
Potential Unlikable Aspects: Remote/ No groceries or food to be purchased outside of summer/ Website difficult for non-Swedes to navigate/ Almost no one around in September, saw 3 or 4 other people the entire time on the island.

5. House LA City Hostel - Füssen, Bavaria, Germany

Dates of Stay: 22-24 October 2014
Why I Liked It: Super cozy hostel/ Comfy beds/ Can see Neuschwanstein Castle from the windows on the upper floor (click middle pic above)/ Views of the Bavarian Alps/ Five minutes from charming downtown Füssen/ Quick ten minute walk to & from train station/ 40 minute walk to & from Schwangau castles (no need to pay for shuttle)/ Near grocery stores.
Potential Unlikable Aspects: Frequently no staff to be found, had to be called by phone/ No kitchen for guest use, we made due making instant mashed potatoes with the help of a hot water kettle in the dining area/ Pay for breakfast.

6. Youth Hostel Pula - Pula, Istria, Croatia

Dates of Stay: 13-17 November 2014
Why I Liked It: Beachfront location with incredibly picturesque views of the Adriatic/ Close to awesome Roman architecture/ Breakfast Included/ Had reduced rates (and hardly any other guests) because November is Croatian off-season/ Hostel Book Exchange.
Potential Unlikable Aspects: No guest-use kitchen, though dinner can be provided for a fee/ In high season, when more people are around, the dorm rooms would definitely feel cramped.

7. Pansion Aldi - Mostar, Bosnia & Herzegovina

Date of Stay: 20 November 2014
Why I Liked It: Welcoming, homey vibe/ Very amicable staff/ Inexpensive laundry service/ Decent kitchen/ Walking distance to Stari Most & Old Town Mostar/ Close to bakeries with delicious goodies/ 4 minute walk from Bus Station.
Potential Unlikable Aspects: It's cold and a wee bit lonely in November.

8. Hostel The Best* - Sarajevo, Bosnia & Herzegovina

Dates of Stay: 21-23 November 2014
Why I Liked It: Located in historic downtown Sarajevo next to Sacred Heart Cathedral/ Upstairs from Galerija 11/07/95, a heart-breaking and enlightening gallery highlighting the atrocity of the Srebrenica massacre/ Minutes from excellent eateries, shops, & historically significant sights/ Fun vibe/ Super helpful staff/ Unlimited free tea for guests in a wide variety of flavors/ Cozy dorm beds/ Very nice bathrooms/ Quite inexpensive.
Potential Unlikable Aspects: Lounge (first picture above on left) could get crowded quickly. No kitchen for guest use.
*Couldn't find a website for this place. According to Google Maps, it's still located at Jelica 2 in Old Town Sarajevo.

9. Bon Paul & Sharky's Hostel - Asheville, North Carolina, USA

Date of Stay: 6 May 2016
Why I Liked It: In a very inviting old home in West Asheville/ Walking distance (or $5 uber) to great restaurants, bars, & nightlife/ Mattresses that are comfier than my bed at home/ Kind, knowledgeable staff/ Nice outdoor deck/ Big kitchen/ Very clean/ Pretty extensive Book Exchange/ Guest book & guest "joke book" in lounge make for fun reads.
Potential Unlikable Aspects: Not a ton of parking available (but cars suck anyway).

10. Mousetrap Backpackers - Paihia, Bay of Islands, New Zealand

Dates of Stay: 3-5 September 2016
Why I Liked It: The owners are number one on my list as far as being the most inviting and helpful hostel staff/ The whole place feels like home away from home/ Great kitchen & lounges that I never wanted to stop chilling in/ Walking distance to shops, eateries, groceries, & ferry/ Book exchange full of books/ Well-maintained and very clean.
Potential Unlikable Aspects: Limited wifi, though that seems to be the NZ standard.
 

11. On the Beach Backpackers - Whitianga, Coromandel, New Zealand

Dates of Stay: 5-7 September 2016
Why I Liked It: Pretty rad beach views/ Relaxing vibe/ Got a funky two-room beachfront apartment all to ourselves (early September is off-season)/ Congenial & chill staff/ DVD rentals/ Close to tourist attractions like Hot Water Beach & Cathedral Cove/ Walking distance to shops & restaurants/ Hot Water Beach shovels for hire/ Kitchens in private rooms and dorm lounge area.
Potential Unlikable Aspects: Limited wifi/ A bit expensive, even for New Zealand standards/ Challenging to get to area attractions without a vehicle.

12. Funky Green Voyager - Rotorua, New Zealand

Dates of Stay: 11-13 September 2016
Why I Liked It: Cheeky decor/ 'Honesty' beer fridge and egg basket/ Family feel/ Excellent hostel kitchen (#1 hostel guest kitchen I've used)/ Super well-maintained/ Easy to book anything in Rotorua at the front desk/ Walking distance to downtown/ Book Exchange.
Potential Unlikable Aspects: Limited wifi/ While common areas are well-decorated and inviting, individual rooms are a little sparse and cold in contrast.