Iznik, Spanaca, or other?

Iznik would be my choice.The lake is lovely and the town itself is interesting wthout being too touristy.Sapance Lake is beautiful but there isn't much else to do there other than walk around it,so I think 2 days there would leave you a bit bored.
From Iznik you are also close enough to go and visit Bursa too so you could make this a very interesting and worthwhile 2 day side trip.

So 2 nights Iznik and 1 night Bursa?

What's it like in Iznik besides the touristy stuff? Can I just chill by the lake and read? Is there hiking?

Iznik is an ancient city originally called Nicaea and is famous for those fabulous blue ceramic tiles that adorn such as Istanbul's Blue Mosque,so it has both Byzantine and Ottoman heritage.Very recently the remains of a basilica were discovered in the lake under only something like a metre of water!
Much of it's historical past still remains including it's four city gates(Lake Gate will lead you to the lake) (obviously!) and much of the walls too.You can visit Aya Sofya ,14th century Green Mosque,plus other mosques and churches and the museum which is small but very interesting and there are ceramic workshops and atölyes you can visit too,oh an a Roman theatre.
I doubt it will still be warm enough but if the weather is kind to you you can swim safely in the lake and take walks around it.The scenery is truly lovely,but as it is a big lake you probably won't have time to cover all of it..
Iznik really has a fascinating history so I would recommend you do some research before you go which will help to bring this nice town to life for you.Who knows?You may not reach Bursa :) Because tourism isn't overdone there I am almost reluctant to share this with others haa haa!

http://www.hurriyetdailynews.com/underwater-basilica-in-turkeys-iznik-to-open-for-visits-.aspx?pageID=238&nID=103674&NewsCatID=375
http://www.iznik.bel.tr/galeri.php

Enjoy!

Thanks so much for your help! What's a good place to stay at by the lake? Budget is not an issue and i'd like the place to have a nice area for relaxing and reading

I've stayed at Grand Hotel Belekoma. It has a nice location on the lakefront road. There are numerous restaurants and cafes nearby and it's very close to the city center.

Your choice of İznik over Spanca is a good one. As Sarikinarya said, once you've looked around the lake at Spanca you've pretty much done everything there is to do. İznik however is a very interesting place to explore. The old hamam there is very good.

No hotel is that expensive in Iznik,so even if you wanted to spend a lot it is not necessary :) 4 hotels come to mind that are right on the lake edge offering both lake and countryside views,and each set in lovely gardens too.In order of the choice I personally would put them-
Limnades Hotel
Çamlık Motel
Seyir Boutique Hotel
Zeytin Bahce Hotel
None of these should be more than 50€ per night including breakfast but don't be put off by these seemingly cheap prices,they are all really very nice places to stay,and as far as I know they all offer bicycle and canoe hire too :) Check around review sites and see which one appeals to you the most.

Hello,

There are tens of non-profit trekking groups that have day-trips and camps. At the end of the trip we share the cost. Typically 20-30 Euros
It ofter includes barbeque with local village meatballs. My favourite group is dogagezginleri@gmail.com you can join their maillist. Quite a few times i saw foreigner guests, i guess they were invited by an existing member. But it is a tottally open group i am sure they would be more than happy to host you. We go to 3 main destinations: IZNIK LAKE ... SAKARYA.... KIRKLARELI (WEST OF ISTANBUL).. a few other groups i can think of are POYRAZ, TREKIST..

Hope you enjoy it.

GREAT to know! Thank you fatmak!!!

Thank you all!