Hi Wilson,
I'm a Latvian myself, and although I've got my licence in Ireland and I have never been involved with any of the schools, I hope I will be able to help you a bit.
Aviobaltica is a small school in Liepaja - it's a small sea-side town in west of the country. It's a rather grim looking town with not much to offer, it is also known as the windy city. It's the perfect spot for if you want to learn sailing or kite-surfing.. not sure about flying, but they just renovated Liepaja airport, so I expect the facilities to be somewhat ok.
I've never heard of avioservice before, their website doesn't look entirely helpful either. If they're a one aircraft operation, be careful, as that one aircraft might go tech and your training can get interrupted.
Generally the top school in the country would be considered
ERIVA
too bad their page doesn't seem to be in English but I'm sure if you send them an email or give them a call they will answer all your questions. For what I know their facilities are very good and they've been around for a long time.
What you need to consider is the climate. Generally October till December is somewhat mild but with very low almost everlasting cloud base with occasional fog/mist showers that turn into sleet/snow late in the year. You'll not do much flying around this time of year. January sees high pressure settle in and you see a lot of CAVOK days but the air temperatures go bitterly cold. While it makes for smooth flying it also can become uncomfortable for yourself if you do not like -20°C or lower.
Daylight during winter is sparse - albeit technically you get around 6.5 hours of daylight, because of the latitude and cloud it really gets dark sooner and you're realistically looking at just some 4-5 hours of usable daylight during the peak of the winter.
Seasons change rapidly and beginning from April/May you can experience very pleasant weather, with lots of daylight, generally dry and CAVOK most days. June can be rainy, July and August have their hot spells of +30°C and above. Thunderstorms, microbursts and even tiny tornadoes can develop very rapidly out of nowhere so expect the course to focus on the weather a LOT! Days are LOONG in summer and one can expect just over 18 hours of usable daylight during peak of the summer..
I have no doubt that the training offered is top notch, however would I recommend a foreigner going through all the hassle, uncertainty with the weather simply to save 1 or 2k for the PPL? I don't know.. hour building is a different story - go in summer, you'll have lot's of fun, you can get cheap solo rates if you ask around. Some private owners are well happy to rent their mogas certified SEPs for as little as 70-80 eur ph/dry
Generally what I would strongly advise you (for a PPL anyway) is do your training where you plan to do most of your flying! You will get to know people and knowing people helps you rent aircraft cheap or participate in fly-ins / fly-outs and other flying activities that otherwise you wouldn't be invited to simply because nobody knows you.